Abstract This paper explores the relationship between firm performance, measured by Tobin's Q and very powerful controlling shareholders in a sample of Belgian listed firms. The paper shows that overall the largest shareholders have a negative effect on firm performance. Nevertheless, in family firms the effect of large controlling shareholders on performance is positive except when they are organized in voting blocks. Firms related to coordination centers display higher performance associated with large shareholders. The paper shows that the presence of a second shareholder in the firm has no significant effect.