Supporting on recent theoretical approaches to the concept of familiness based on the notion of social capital, this study analyzes the composition of top management teams in non-listed family firms and its effect on the performance of these firms. An empirical analysis comprising 929 Spanish private family firms highlights the positive and significant influence of the inclusion of non-family managers, the family nature of top executives, as well as the presence of the founder. The study includes no significant results regarding homogeneity within family managers, or the interaction between a top family executive and the proportion of non-family managers.