This study investigated the relationship between insider ownership and firm performance in the restaurant industry. Convergence-of-interests and entrenchment hypotheses were tested via cross-sectional and panel two-stage least square (2SLS) GMM estimation methods for linear and non-linear models. The study found that there is an overall positive and significant relationship between insider ownership and firm performance. The quadratic model showed that restaurant firm performance increased until insider ownership was between 38 and 40%, whereas it decreased after that point. Consistent with the quadratic model, the piece-wise regression model showed that insider ownership had a positive impact on firm performance within a range of 5–25% and a negative influence beyond 25% insider ownership. Consequently, this study revealed that convergence-of-interests and entrenchment effects of insider ownership co-exist in the restaurant industry. While convergence-of-interests effects are effective, an excessive granting of stock options or awards to managers could weaken firm performance due to entrenchment effects.