How do board composition and board ties influence the performance of startups? An immense body of literature on boards of directors with a predominant focus on large and mature firms remains largely inconclusive to the impact of boards on performance. In this paper, we argue that boards of directors provide means of startups to access expertise and gain legitimacy. We develop a set of hypotheses related to board size, turnover and interlock ties with similar and dissimilar organizations and test this with a comprehensive longitudinal dataset from Sweden. The results suggest that direct board ties to similar organizations have a positive effect whereas board ties to dissimilar organization have a negative effect on performance. Surprisingly, we find no consistent results of the effects of board structure. We discuss the implications for theory and practice.