Studies have suggested that members of ethnic minority groups might be healthier when they live in areas with a high concentration of people from their own ethnic group - in spite of higher levels of material deprivation typically found within such areas. We investigated the effects of area-level same-ethnic density on maternal and infant health, independent of area deprivation and individual socioeconomic status, in five ethnic minority groups. The study was a cross-sectional analysis within the UK Millennium Cohort Study and included mothers in five ethnic minority groups (Black African n=367, Bangladeshi n=369, Black Caribbean n=252, Indian n=462 and Pakistani n=868) and their 9-month-old infants. Outcome measures included: low birth weight, preterm delivery, maternal depression, self-rated health and limiting long-standing illness. Compared to those who live in areas with less than 5% of people from the same-ethnic minority population, Indian and Pakistani mothers were significantly less likely to report ever being depressed in areas with high same-ethnic density. There was a protective effect of ethnic density for limiting long-term illness among Bangladeshi mothers at 5-30% density and Pakistani mothers at all higher densities. Ethnic density was unrelated to infant outcomes and maternal self-rated health, and unrelated to any outcomes in Black African and Black Caribbean mothers and infants, possibly because no families in these groups lived at higher levels of same-ethnic density. Results were similar whether we examined smaller or larger residential areas. We conclude that, among ethnic minority mothers and infants in England, the relationship of ethnic density to health varies by ethnicity and outcome. For some measures of maternal health, in some ethnic groups, the psychosocial advantages of shared culture, social networks and social capital may override the adverse effects of material deprivation.