Many different medical school selection processes are used worldwide. In this paper, we examine the effect of (1) participation, and (2) selection in a voluntary selection process on study performance. We included data from two cohorts of medical students admitted to Erasmus MC, Rotterdam and VUmc, Amsterdam, The Netherlands and compared them to previously published data from Groningen medical school, The Netherlands. All included students were admitted based on either (1) a top pre-university grade point average, or (2) a voluntary selection process, or (3) weighted lottery. We distinguished between lottery-admitted students who had participated in the voluntary selection process and had been rejected, and lottery-admitted students who had not participated. Knowledge test scores, study progress, and professionalism scores were examined using ANCOVA modelling, logistic regression, and Bonferroni post hoc multiple-comparison tests, controlling for gender and cohort. For written test grades, results showed a participation effect at Groningen medical school and Erasmus MC (p < 0.001), and a selection effect at VUmc (p < 0.05). For obtained course credits, results showed a participation effect at all universities (p < 0.01) and a selection effect at Groningen medical school (p < 0.005). At Groningen medical school, a participation effect seemed apparent in on time first-year completion (p < 0.05). Earlier reported selection and participation effects in professionalism scores at Groningen medical school were not apparent at VUmc. Top pre-university students performed well on all outcome measures. For both the participation effect and the selection effect, results differed between universities. Institutional differences in curricula and in the design of the selection process seem to mediate relations between the different admissions processes and performance. Further research is needed for a deeper understanding of the influence of institutional differences on selection outcomes.