Mental health problems are common in primary care, with prevalence rates of up to 40% reported in developing countries. The study aim was to evaluate the impact of a specially designed toolkit used to train primary health care (PHC) workers in mental health on the rates of diagnosed cases of common mental disorders, malaria and non-specific musculoskeletal pains in primary care in Malawi.

Clinics with out-patient services in the designated district were randomly divided into control and intervention arms. Using a two-phase sampling process, Self-Reporting Questionnaire scores, data on diagnoses made by PHC workers and results of the Structured Clinical Interview for DSM-IV for depression were collected from 837 consecutively attending adult patients in the pre-intervention study and 2600 patients in the post-intervention study.

The point prevalence rates for probable common mental disorder and depression were 28.8% and 19%, respectively. Rates for both anxiety and depression diagnoses by PHC workers at baseline were 0% in both arms. Following training, there were significant differences between the two arms in the rates of diagnosed cases of depression [9.2% v. 0.5%, odds ratio (OR) 32.1, 95% confidence interval (CI) 7.4–144.3, p ⩽ 0.001], anxiety (1.2% v. 0%, p ⩽ 0.001) and malaria (31% v. 40%, OR 0.62, 95% CI 0.43–0.89, p = 0.01). The intervention arm had more cases diagnosed with depression and anxiety while the control arm had more cases diagnosed with malaria.

Training of PHC workers in mental health with an appropriate toolkit will contribute significantly to the quality of detection and management of patients seen in primary care in developing countries.