OBJECTIVE: This study aims to investigate whether there are differences in the prevalence of common mental disorders and social capital between migrant and non-migrant groups in Peru. METHODOLOGY: The PERU MIGRANT study is a cross-sectional study comprising three groups: an urban group from a shanty town in Lima; a rural group from a community in Ayacucho-Peru; and a migrant group originally from Ayacucho currently living in the same urban shanty town. Common mental disorders were assessed using the General Health Questionnaire (GHQ-12), and social capital was assessed using the Short Social Capital Assessment Tool (SASCAT). Poisson regression with robust standard errors was used to estimate prevalence ratios. RESULTS: The overall prevalence of common mental disorders was 39.4%; the highest prevalence was observed in the rural group. Similar patterns were observed for cognitive social capital and structural social capital. However after adjustment for sex, age, family income and education, all but one of the significant relationships was attenuated, suggesting that in this population migration per se does not impact on common mental health disorders or social capital. CONCLUSIONS: In the PERU MIGRANT study, we did not observe a difference in the prevalence of common mental disorders, cognitive and structural social capital between migrant and urban groups. This pattern of associations was also similar in rural and urban groups, except that a higher prevalence ratio of structural social capital was observed in the rural group.