The recent influx of migrants and refugees into Europe and elsewhere raises questions as to whether migrant behavior reflects cultural predispositions and whether assimilation through exposure to host institutions can be expected. The paper focuses on financial behavior and uses high-quality administrative data on migrants and refugees to Sweden. It uncovers differences across cultural groups in how behavior relates to household characteristics, and shows that differences diminish with exposure to host country institutions, even for large cultural distances. Interestingly, robust cultural classification of European countries based on genetic distance or on Hofstede’s cultural dimensions fails to identify a single “southern” culture but points to a “northern” culture. Our results also have implications for the potential of European institutional harmonization, exogenously imposed during the fiscal crisis, to alleviate cultural differences in financial behavior.