BACKGROUND: Traditional perinatal practices may protect against postnatal common mental disorders (CMD) in non-Western societies. AIMS: To evaluate the association between perinatal practices and postnatal CMD in rural Ethiopia. METHOD: A population-based sample of 1065 women was followed up from pregnancy until 2 months postpartum. Qualitative investigation informed the development of scales measuring attitudes towards and adherence to perinatal practices. Postnatal CMD was measured using the Self-Reporting Questionnaire. RESULTS: Endorsement of sociocultural perinatal practices was associated with lower odds of antenatal CMD persisting into the postnatal period (adjusted odds ratio (OR) = 0.66, 95% CI 0.45-0.95). Women who endorsed protective and celebratory perinatal practices but were unable to complete them had increased odds of incident (adjusted OR = 7.26, 95% CI 1.38-38.04) and persistent postnatal CMD (adjusted OR = 2.16, 95% CI 1.11-4.23) respectively. CONCLUSIONS: There is evidence for an independent role of sociocultural practices in maintaining perinatal mental health in this Ethiopian community.