Interethnic ties are considered important for the cohesion in society. Previous research has studied the determinants of interethnic ties with cross-sectional data or lagged panel designs. This study improves on prior research by applying multilevel growth curve modelling techniques with lagged independent variables, which provide better estimates of causal relationships than methods previously applied. Longitudinal data are used from the German Socio-Economic Panel (GSOEP), covering a 15-year period. The study analyses within- and between-person differences in contacts with native Germans for Turkish, (ex)Yugoslav, Spanish, Italian and Greek immigrants in Germany. Immigrants who learn the German language and get employed are more likely to subsequently establish contacts with Germans. Furthermore, immigrants who intend to settle permanently in Germany develop more interethnic ties than those who intend to return. No evidence is found for investments in education. The multilevel growth curve models not only confirm some of the earlier established determinants, but also question the causal impact of others.