Utilizing a large sample of South Korean firms, this paper explores the impact of corporate governance in an emerging market country dominated by a few large business groups. Firms affiliated with the top five groups (chaebol) exhibit significantly lower performance and significantly higher sales growth relative to other firms. Furthermore, top executive turnover is unrelated to performance for top chaebol firms, indicating a breakdown of internal corporate governance for the largest business groups. Internal corporate governance appears much more effective for firms unrelated to the top chaebol as managers at poorly performing firms are significantly more likely to lose their job. These results imply that the lack of properly functioning internal corporate governance among the top chaebol, which dominate the Korean economy, may have increased the severity of the recent financial crisis.