Concurrent partnerships have been recognized as a determinant for the spread of HIV and sexually transmitted infections (STIs). We studied the association of concurrent partnerships with sexual behaviour among heterosexual Caribbean and African migrants, who account for a disproportionate burden of STIs and HIV in the Netherlands. Of 1792 migrants, 15% reported concurrent sexual partners in the previous six months. In multivariate multinomial analyses, women were less likely to have concurrent partners than men and they were less likely than men to use condoms with concurrent partners. We could not identify an association with the observed HIV prevalence; however, migrants with concurrent partners were less likely to be tested for HIV. Of migrants tested for STIs, one in three migrants with concurrent partners was diagnosed with an STI. Prevention targeting migrants should address the promotion of HIV/STI testing and stress the potential acceleration of HIV and STI epidemics due to concurrency.