This paper evaluates the impact of ownership concentration on firm performance in a weak institutional environment. Specifically, using new survey evidence, we seek to appraise quantitatively the performance of block-holder-controlled firms in Russia and to identify, within the domain of corporate governance theory, factors that may explain such performance. We find evidence of negative association between the size of the dominant owners’ shareholding and performance parameters such as investment, capacity utilization, and profitability. At the same time, we establish that control structures with multiple, large shareholders increase efficiency. The ambiguity of the effects of ownership concentration suggests that country-specific factors play an important role.