When a top-performing fund closes to new investors, there are often few worthwhile alternatives run by the very same management team. But that’s not the case for Vanguard’s perennially closed PRIMECAP funds. The same sub-advisor— PRIMECAP Management Co— actually offers three funds open to new investors under its own label. Even better, its PRIMECAP Odyssey Aggressive Growth (POAGX) has not only more than doubled investors’ money since its 2004 launch, it has also outperformed the five other PRIMECAP-managed funds by a wide margin.

Part of POAGX’s edge over its PRIMECAP peers is likely due to its focus on smaller, fast-growing equities, a specialty that’s unique among PRIMECAP’s traditional lineup of large-cap growth funds. Of course, the fund’s seasoned management team and contrarian approach to stock selection likely deserve most of the credit.

Similar to other value-conscious growth funds, management looks for stocks that are out of favor with the market, but offer the possibility of growth at a reasonable price. Additionally, the fund’s four co-managers have decades of experience, and all but one have been with the fund since inception. The fund’s management is also impeccably credentialed: Three of the four co-managers have science or engineering degrees and all four are Harvard MBAs.

PRIMECAP fosters a culture of the individual, as opposed to the committee. Each of the fund’s co-managers independently runs a portion of the fund, bringing to bear his unique background and insights. Even with such autonomy, PRIMECAP’s managers are expected to share ideas with their colleagues, and this can lead to a heavy emphasis on favored sectors.

Recently, for example, almost 50 percent of the fund’s assets were in healthcare stocks, and close to 30 percent in technology. In a June 2012 letter to shareholders, management noted that the US technology sector is benefiting from a surge in innovation, strong balance sheets and relatively low valuations; healthcare is benefiting from an uptick in FDA approvals, and new types of drug creation and delivery systems.

Although the portfolio is heavily tilted toward smaller-cap names, it still holds some giants, such as Swiss pharmaceutical Roche Holding AG (OTC: RHHBY) and Google (NSDQ: GOOG). But the overall focus is on smaller fare, such as Seattle Genetics (NSDQ: SGEN), which is developing cancer-fighting drugs based on antibodies, and Shutterfly (NSDQ: SFLY), an online photo-management site.

Management takes a long-term perspective toward investing, so they buy with conviction once they’ve identified a promising name. While other growth funds tend to trade excessively, POAGX has an annual turnover rate of just 11.3 percent.

POAGX has trounced the market over the past five years, gaining 18.6 percent annualized, versus 14.6 percent annualized for the S&P 500. Although the fund achieved this performance while incurring substantially greater volatility than the market, it still managed to beat the market by a sizable margin on a risk-adjusted basis. This means the fund’s investors are well compensated for enduring the portfolio’s swings in value.

The bottom line: POAGX is an excellent option for long-term investors who need mid-cap exposure and missed out on investing in the firm’s Vanguard-branded funds.