There is a renewed interest on the need to strengthen mechanisms to ensure that managers and directors take measures to protect the interest of a firm’s stakeholders. This study made use of panel data regression analysis between 2002 and 2006 for a sample of 62 firms listed on the Nigerian Stock Exchange to examine the relationship between internal and external governance mechanisms and corporate firms’ performance. The results have the implication that regulatory agencies should encourage firms to achieve a reasonable board size since overly large boards may be detrimental to the firm. Our results also show no significant evidence to support the idea that outside directors help promote firm performance. In addition, the study found that the measure of performance matter for analysis of corporate governance studies. We found in some cases different results from the use of Returns on Assets (ROA) and Tobin’s Q as measures of firm performance.