The 10 best-performing stocks of the past decade were obscure, ignored, and small. But what about the top 25? The top 50? The top 100?

It turns out that most of the stock market's greatest performers of the past 10 years were also obscure, ignored, and small.

Small stocks for big returns
There were 325 stocks that could have earned you greater than 20% annualized returns from 1996 to 2005 -- turning a $10,000 initial investment into more than $60,000. Of those 325 stocks, 296 of them were small caps. That's more than 90%. While the companies run the gamut from homebuilder DR Horton (NYSE:DHI) to mobile-home parts maker Drew Industries (NYSE:DW), the common thread is size.

Ten years ago, DR Horton was a regional homebuilder with a small $1 billion market cap. Today, it's a $10 billion national name. Drew Industries grew from a $100 million valuation, rewarding shareholders along the way.

And Drew Industries, for one, is still growing. The company dominates its niche and has almost every trait investors should look for in a small cap: superior leadership, clear competitive advantages, a strong corporate culture, and superior returns on equity (approaching 21% over the trailing 12 months). Since we recommended it in our Motley Fool Hidden Gems newsletter, it has also returned 37% for our members -- but we're confident it will keep on performing over the long term.

Big stocks for smaller returns
There were only 29 mid- or large-cap companies that would have given you the same growth, and they're the cream of the crop: Harley-Davidson (NYSE:HOG), EMC (NYSE:EMC), and Nokia (NYSE:NOK), to name three. And while the returns have been incredible from these three companies -- all of which demonstrate some key traits of great small caps: strong brand, strong competitive position, strong leadership -- they just don't stack up against the small guys.

That's because it's difficult for larger companies to generate the same kind of growth as small caps. During the 10 years from 2005 back, Drew Industries grew from $100 million to $700 million. Nokia, on the other hand, grew from a $12 billion valuation to $80 billion. While Nokia added substantially more value in absolute terms, the story changes when it comes to percentages. Drew increased more than 600% to Nokia's 570%. Now compare that with much larger companies such as ExxonMobil (NYSE:XOM) or Intel (NASDAQ:INTC). Those two companies added $200 billion and $100 billion of value, respectively, during the same 10-year span. But those increases resulted in just 250% gains for investors. That's a consequence of the Law of Diminishing Returns, and it's a simple and crucial point in investing.

Fool's final word
Small caps are one area of the market where the individual investor has the opportunity to earn phenomenal returns, but there are also pitfalls. For every one of the 296 small caps that could have earned you greater than 20% annualized returns over the past 10 years, there were quite a few more that didn't make it. Small-cap stocks tend to carry considerably more risk than large caps, so investors must consider their investments very carefully.

That's why we advocate a diversified portfolio of select small caps for Hidden Gems subscribers. By focusing on factors like superior management and a strong balance sheet and enjoying the benefits of diversification, our small-cap recommendations have outperformed the market by more than 21 percentage points since we started.

Every investor should have at least some smart exposure to small caps, because the historical profits are just too good to pass up. If you'd like some help getting started in this incredible area of the market, click here to join our community free for 30 days.

This article was originally published on Feb. 6, 2006. It has been updated.

Tim Hanson does not own shares of any company mentioned. Intel is a Motley Fool Inside Value recommendation. No Fool is too cool fordisclosure.