The existence of restricted shares has significant implication for a potential divergence of interest between external equity providers and "insiders", and the deeper the divergence, the greater the potential for underperformance. Application of this agency theory to "singles" suggests a lower performance compared to "matched" diversely-held firms. Based on a sample of 90 internally-controlled restricted voting firms with their corresponding "matched" firms identified using propensity scores, this study provides partial empirical support to theoretical implications. Between 1985 and 1994, Treynor's performance index of 0.012 and 0.011 for "singles" and "matched" firms respectively, confirms no significant statistical difference in long term stock market performance. Accounting-based analysis is also consistent with stock market performance, however, when the sample of Initial Public Offerings is analysed separately, "matched" firms actually outperform "singles".