The ability to detect mental disorders varies greatly among general practitioners in primary health care. The aim of this study was to determine the factors underlying the differences between general practitioners in the ability to recognize mental disorders in Finnish patient populations. The group studied consisted of 1000 randomly selected adult patients of primary care facilities in the city of Turku. The Symptom Checklist (SCL-25) was used as the reference method in the identification of psychiatric cases. According to the SCL-25, one fourth of the sample had mental disorders. A good recognition ability was associated with postgraduate psychiatric training and qualification as a specialist in general practice. Surprisingly, Balint group training, which is a method intended to improve the ability of general practitioners to manage their patients' mental health problems, was associated rather with poor than good detection ability.