The concept of social capital is increasingly used in entrepreneurship studies to explain the growth of innovative nascent firms. However, empirical findings about the role of social capital (SC) in the growth of young firms have been contradictory to date. We focused on the relational dimension of social capital and differentiated between internal social capital (ISC) and external social capital (ESC). We analysed the perceived utility which is rarely used in SC studies of resources received from the networks of innovative nascent firms in their first six years of existence. We implemented the two-stage least squares (2SLS) analysis to avoid the endogeneity bias. The results indicated that during the early years, nascent firms' external social capital is a decisive resource for growth. This was not the case for internal social capital. We observed that joining an incubator appears to have no impact on either growth or the relationship under study.