The increasing importance of knowledge for the development of firms and territories has enhanced the interest in knowledge-intensive business services (KIBS). Drawing on the intrinsic features of KIBS (a strong knowledge base and an extended network of partners and clients), this paper aims to contribute to the literature on entrepreneurship by examining the extent to which entrepreneurs' human and social capital support their KIBS firms' performance at different stages of their organizational life-cycle. Based on a sample of Italian KIBS companies, human capital was found to affect a firm's performance during its early development, whereas social capital took the fore during its expansion. We discuss the implications for research on entrepreneurship and KIBS development policies.