This study investigates the factors that influence the growth rate of firms in Nigeria with a sample of 94 publicly listed firms during the period 1994-2005. The theoretical/analytical framework rested on the optimal firm size growth theory. It offers the most practical approach. The empirical methodology combines descriptive/statistical with econometric analysis. The significant determinants of the firms’ growth rates include the firms’ previous growth rates, size, age, capital intensity, financial constraints, management efficiency, and the extent of vertical integration. However, the significance of these factors depends on how the growth of firm is defined and/or measured as well as the estimation methods.