To compare the association between neighborhood Latino immigrant concentration and infant mortality by maternal nativity among singleton births to Mexican-origin women in Los Angeles County. Information about births, infant deaths, and infant and maternal characteristics were obtained from geocoded Los Angeles County vital statistics records (2002-2005). Linked data on neighborhood characteristics (census tracts) were obtained from the 2000 census. Logistic regression models were used to predict infant mortality while accounting for spatial clustering by census tract. Two-thirds of births to Mexican-origin mothers were to foreign-born women. Foreign-born mothers were older, had less education, and were more likely to have delivery costs paid by Medicaid than US-born mothers. Infants born to foreign-born women had a lower infant mortality rates than infants born to US-born women (3.8/1,000 live births vs. 4.6, p = .002). Among infants of foreign-born mothers, the odds of infant mortality increased with increasing immigrant concentration (OR 1.29; 95 % CI 1.01-1.66). There was a similar pattern of association between immigrant concentration and mortality for infants of US-born mothers (OR 1.29; 95 % CI 0.99-1.67). In Los Angeles County, the odds of infant mortality among foreign-born Mexican-origin Latina were higher in higher-density immigrant neighborhoods, with a similar trend among US-born mothers. Thus, living in immigrant enclaves likely does not help to explain the lower than expected infant mortality rate among infants born to Latina women. Instead, higher neighborhood Latino immigrant concentration may indicate a neighborhood with characteristics that negatively impact maternal and infant health for Latinos.