Objective  To examine Nepali migrants’ vulnerability to HIV/sexually transmitted infections (STIs) and their possible role in causing the epidemic in far western Nepal. Methods  From August to October 2000, we conducted six focus group discussions among 53 returned migrants from India, mainly from Mumbai. Data were analysed by interpretative thematic analysis. Results  Migrants commonly had multiple sexual encounters, changed partners, and used condoms infrequently both in India and at home. Several factors influenced them to practice high-risk sexual behaviours. In India, these included peer norms and pressures, cheaper sex, lack of family restraint, drinking alcohol, and low perceived vulnerability to HIV/STIs. In Nepal, these factors included the migrants’ new status, frequent local festivals, and low perceived vulnerability to HIV/STIs. Participants displayed substantial deficits in their knowledge of HIV/STIs. Conclusions  This study revealed Nepali migrants’ high-risk sexual behaviours both abroad and at home. Understanding these realities will assist in the development of culturally appropriate HIV/STI interventions necessary to halt the spread of HIV/STIs in Nepal.