We investigated whether the language of instruction (Dutch or English) influenced the study success of 614 Dutch and German first-year psychology students in the Netherlands. The Dutch students who were instructed in Dutch studied in their native language (L1), the other students in a second language (L2). In addition, only the Dutch students studied in their home country. Both these variables could potentially influence study success, operationalised as the number of European Credits (ECs) the students obtained, their grades, and drop-out rates. The L1 group outperformed the three L2 groups with respect to grades, but there were no significant differences in ECs and drop-out rates (although descriptively, the L1 group still performed best). In conclusion, this study shows an advantage of studying in the L1 when it comes to grades, and thereby contributes to the current debate in the Dutch media regarding the desirability of offering degrees taught in English.