You know who you are. I've been knocking around this business for years, and everywhere I've stopped I've met someone like 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 few weeks 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.

Unlike small caps -- say, anything with a market cap between $150 million and $2 billion -- 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 all occurred to me when Tom Gardner began highlighting micro caps in his Motley Fool Hidden Gems newsletter service. I about went out of my mind. No offense to my rumor mill, but I don't have to tell you how hard it is find good information on tiny companies. And talk about right up my alley.

Which isn't to say the old gang didn't score from time to time. Mark from New York turned up tiny Alliance Gaming (NYSE:AGI) back in January 2000. It's up more than 5,000% since. I can't remember who, but somebody chimed in with Taser (NASDAQ:TASR) not more than a year or so back. I sure wish I'd taken that call.

There were others, too. But in a sense, we're just winging it. With tiny gems the focus is firmly on profitability and value. The rumor mill deals largely in speculations. How many of you have pointed out that I still own Applied Digital (NASDAQ:ADSX), for Pete's sake? 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 (NYSE:WMT). Who would imagine that Sam Walton's empire once boasted a market cap of less than $30 million? Yet even then the company was making money. It was shareholder-friendly, conservatively managed, and heavily owned by obsessive founders.

If you'd invested $5,000 in Wal-Mart in 1970, you'd be sitting on about $26 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; and
  • 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. If nothing else, a dividend implies 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. Telecom giant Qualcomm (NASDAQ:QCOM) is off its highs, but if you'd bought it in 1991, you'd be sitting on 10,000% gains. Amgen (NASDAQ:AMGN) was once a micro, as was Dell Computer (NASDAQ:DELL). Had you bought Dell 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 on Dell 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 to the $2 million if you'd pulled the trigger back in 1990.

Do you really need proof?
Of course, I can't claim with any certainty that micro-cap stocks will continue to outperform over the next 20 years. I can't even promise that micro-cap value stocks will. But I assure you that 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 to 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 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.

Keeping my promise to you
I promised to keep you posted on Hidden Gems' performance. As of February 3, 2005, the recommendations are up, on average, 42.5%. That's compared to 8.9% if you'd invested in the S&P 500 for the same period. For context, that's 40 picks over 20 months.

As for tiny gems, it's still early. Plus, these are not formal recommendations and so are not currently tracked on the scorecard. But it shouldn't surprise you that members are tracking their performance on our discussion boards. Here are some early, unofficial results:

As of January 29, the 12 tiny gems featured in Hidden Gems were up 18.4% on average. That's compared to a 2.4% gain for the S&P 500 and 4.4% for an impressive benchmark, the Bridgeway Ultra-Small Company Market Fund. So far, so good. Thanks for running the numbers, FoulWeather.

What to do now
You can bet I will follow up on this thread. 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 check out what's going on at Hidden Gems? There's a regular feature dedicated to micro caps, and the tiny gems board is superactive. Best of all, Tom is offering a free 30-day trial -- that way you can see if it's right for you, without betting the farm. Click here to learn more.

Fool writer Paul Elliott owns shares of Applied Digital. The Motley Fool has a full disclosure policy.