In this paper we analyze the effect of outside university work on time to first degree at German universities. The database is the "Absolventenpanel" 2001, a panel study conducted by the "Hochschul-Informations-System". Aiming to estimate the causal effect correctly, we apply a matching strategy based on the approach put forward by Rosenbaum and Rubin [(1983) "The Central Role of Propensity Score in Observational Studies for Causal Effects." "Biometrika" 70: 41-55]. The results of the matching approach reveal that simple prima facie results are upward biased but confirm that off-campus work has a prolonging effect on study duration.