Background: The optimum way to improve the recognition and treatment of postnatal depression in developing countries is uncertain. We compared the effectiveness of a multicomponent intervention with usual care to treat postnatal depression in low-income mothers in primary-care clinics in Santiago, Chile. Methods: 230 mothers with major depression attending postnatal clinics were randomly allocated to either a multicomponent intervention (n=114) or usual care (n=116). The multicomponent intervention involved a psychoeducational group, treatment adherence support, and pharmacotherapy if needed. Usual care included all services normally available in the clinics, including antidepressant drugs, brief psychotherapeutic interventions, medical consultations, or external referral for specialty treatment. The primary outcome measure was the Edinburgh postnatal depression scale (EPDS) score at 3 and 6 months after randomisation. Analysis was by intention to treat. This study is registered with C