The purpose of this pretest-posttest study was to evaluate effects of a training program designed to improve primary care physicians' (PCPs) ability to recognize mental health problems (MHP) and to diagnose and manage depression according to clinical guidelines. The primary care settings were in the northern part of The Netherlands. There were eight intensive, hands-on training sessions of 2.5 hours, each of which three were targeting depression (7.5 hours). In the pretraining phase we screened 1778 consecutive patients of 17 PCPs with the 12-item General Health Questionnaire (GHQ-12) and interviewed a stratified sample of 518 patients about presence of current depression with the Primary Health Care version of the Composite International Diagnostic Interview (CIDI-PHC). PCPs registered patient's mental health (status, severity, diagnosis) and treatment prescribed. Then we trained the PCPs. In the posttraining phase, we screened a new group of 1724 consecutive patients of the same PCPs and a new stratified sample of 498 patients went through the same interview and rating procedures as patients in the pretraining phase. Knowledge about depression was assessed pre- and posttraining. PCPs' knowledge of depression improved significantly. Recognition of MHP and accuracy of depression diagnosis improved, but was not statistically significant. The proportion of patients receiving treatment according to the clinical guidelines increased significantly. It was observed that training PCPs improves the management of depression.