You know who you are. I've been knocking around this business for years, and everywhere I've stopped I've met you. And every time I turn up someplace new, I take one or two of you along with me. At least in spirit.

Behold! My own personal whisper-stock-party-tip rumor mill. One day, it's a call from Mark in Rockville. Then it's Sean from Miami or Shannon from Boston. And just when you think you've heard it all, it's the other Mark from New York. He's got to be the worst of the lot.

The greatest stocks of all
A while back, I made the case for "Wall Street's Worst-Kept Secret." In a nutshell, it's that small-cap stocks tend to outperform their larger-cap peers over time -- and that successful stock investors own them. What, then, is Wall Street's best-kept secret?

I'll spare you the drumroll. It's that micro caps do even better. At least a certain type of them do. In a bit, I'll back that up with some hard numbers. Heck, I'll even toss in a few anecdotes, but first some fine print.

Micro caps are not for everyone. They're for people like Sean and Shannon and the Marks. They're for people who love this stuff -- serious investors who have the time and inclination to do some real digging. Or have someone they trust to do it for them.

Tiny Gems
This occurred to me when Tom Gardner began featuring micro caps in his Motley Fool Hidden Gems newsletter. I'd been a fan of the smaller gems previously left to the Watch List. No offense to my rumor mill, but it is difficult to find detailed information on tiny companies.

Which isn't to say the old gang doesn't score from time to time. We did. But in a sense, we are just winging it. With Tiny Gems, the focus is on potential and value. The rumor mill deals largely in speculations. Tiny Gems, by contrast, meet the rigorous Hidden Gems criteria. They're just smaller.

Poor little Wal-Mart?
Love it or hate it, just try to escape Wal-Mart. Who would imagine that Sam Walton's empire once boasted a market cap of less than $30 million? Yet even then the company made money. It was shareholder-friendly, conservatively managed, and heavily owned by obsessive founders.

If you'd invested $5,000 in Wal-Mart in 1980, you'd be sitting on about $2.5 million today. Hindsight is 20/20, of course, but it hardly seems that Wal-Mart was ever a particularly risky investment. After all, it actually paid a dividend, even when it was a small fry. As with any small cap, insist on these in any micro cap:

  • Solid management with significant stakes
  • Great, sustainable businesses
  • Dominant positions in niche markets
  • Sterling balance sheets
  • Strong free cash flow

Just insist twice as hard. Because contrary to how investors behave, the smaller the company, the more important these things are. Best of all, look for micro caps that pay a dividend, like Wal-Mart did. A dividend implies a lot of good things, including that the company won't be out begging for new capital -- a great sign if ever there was one.

Many fish in the sea
And it's not just Wal-Mart. Consider Best Buy (NYSE:BBY) or Target (NYSE:TGT). Both looked pretty solid by January 1990. If you'd bought them then, you'd be sitting on 14,000% and 5,000% gains, respectively. You could have bought American Eagle Outfitters (NASDAQ:AEOS) -- an original rumor mill find -- as recently as 1997 for similar 5,000% gains.

The rise and fall of AOL (now part of Time Warner (NYSE:TWX)) is the stuff of legends. Investors who bought at the top have thus far been sorely disappointed. Those who bought it back in 1994, however, are still sitting on obscene profits. And then there is Dell (NASDAQ:DELL). Had you bought back in 1990, you'd be up some 40,000%.

But here's the thing: Those first few doubles and triples matter. If you'd held off just until January 1992, you'd still be sitting on a 15,000% gain. Not too shabby, but consider that your $5,000 investment would be worth $750,000 -- paltry compared with the $2 million if you'd pulled the trigger back in 1990.

Frankly, this all stands to reason. You could buy General Electric (NYSE:GE) and Microsoft (NASDAQ:MSFT) all day long. And maybe you should -- but neither can be the next GE or Microsoft. With market caps in the hundreds of billions, what are the chances either one of those can run up another 1,000% in value? Pretty slim.

What you need is proof
Of course, I can't claim with any certainty that micro-cap stocks will continue to outperform over the next 20 years. Or that we can find the next big winners. I can't even promise that micro-cap value stocks will outperform. But they have done so in the past.

In "Worst-Kept Secret," I made a point of how, since 1926, small-cap stocks have thumped large caps -- with small-cap value stocks faring best. That's according to Ibbotson Associates, which also ran the numbers for micro caps, this time from 1968 to 2002. Turns out micro-cap value stocks take the cake.

Consider: $10,000 invested in micro-cap value back in 1968 had grown to nearly $1,050,000 a quarter-century later. Compare that with around $950,000 for the same amount invested in small-cap value (which, remember, is downright phenomenal) and a mere $180,000 for large-cap growth.

Ride the tiger
For all of that, micro caps are for investors who can stomach a little volatility. OK, a lot of volatility. The stocks of smaller companies are simply more jumpy than all others. There are reasons for this, ranging from low liquidity to uneven news flow to execution glitches associated with rapid growth and sensitivity to the business cycle. Volatility? Expect it.

And when it comes to business or company risk -- heck, even sector risk -- it pays to diversify. My pal Rex Moore here at Fool HQ says to allocate "one full stock position" to a basket of micro-cap stocks. I can't promise I will muster that kind of discipline myself, but I certainly see the value in it. Just be careful.

And here's a crucial point: If you're indexing, you'd better stick with value. There are big winners among the richly valued high growers, but buying micro caps with big P/Es or with no earnings is exponentially more risky. Those Ibbotson numbers I gave you before were for micro-cap value stocks.

Not coincidentally, the same holds for my real-life examples, too. The Hidden Gems approach is to look for growth potential and real earnings -- at a reasonable price. I'm betting that sounds like a whole lot of fine print, warnings, and disclaimers. But did I mention the potential rewards? Out of this world.

Don't think performance doesn't count
I promised to keep you posted on Hidden Gems performance. As of Aug. 9, 2005, the recommendations are up, on average, 32.8%. That's compared with 10.5% if you'd invested in the S&P 500 for the same period. For context, that's more than 50 picks over two-plus years.

As for Tiny Gems, these are not formal recommendations. But it shouldn't surprise you that members are tracking their performance on our discussion boards. Here are some unofficial results: As of Aug. 6, 2005, the 24 Tiny Gems featured in Hidden Gems were up 8.1% on average. That beats a 6.6% gain for the S&P 500 but trails the 11.1% return on a very solid Bridgeway Ultra-Small Company Market Fund. As always, thanks for crunching the numbers, FoulWeather.

What to do now
Micro caps may not be for everyone, but they sure are a blast. And there sure is a lot to talk about. But fear not -- it's not exactly rocket science, either. More than anything, just promise me you'll keep your head ... and diversify.

Or why not try this? Tom will let you try out Hidden Gemsfree for 30 days. He's got a regular feature dedicated to micro caps, and the Tiny Gems board is superactive. Best of all, your trial is free -- that way, you can see if it's right for you without betting the farm. Click here to learn more.

This commentary was originally published on Feb. 4, 2005. It has been updated.

Fool writer Paul Elliott owns none of the stocks mentioned. Dell, Best Buy, and Time Warner are Motley Fool Stock Advisor recommendations. The Motley Fool has a fulldisclosure policy.