Research has demonstrated a correlation between living in a low-income neighborhood and mental health. However, neighborhood variables affecting mental health and the extent they serve as risk or protective factors are not well understood. Using longitudinal data from a representative sample of low-income mothers from the Welfare, Children, and Families: A Three City Study, the trajectories of total mental health, depression, somatization, and anxiety from the Brief Symptom's Inventory are assessed. Then, the effects of two neighborhood concepts-collective efficacy and neighborhood problems-on mental health trajectories are assessed. Results indicate that total mental health, depression, somatization, and anxiety all decrease in this sample over time. Perceiving one's neighborhood to be high in collective efficacy is predictive of healthier trajectories. The presence of neighborhood problems is associated with declines in mental health trajectories. Findings demonstrate the need to address neighborhood conditions to improve mental health for low-income mothers living in low-income neighborhoods. (C) 2014 Wiley Periodicals, Inc.