The epidemiology of mental problems in the Gomel region in the republic of Belarus was studied in a two-stage survey of a broad based population sample (N = 1617), using the General Health Questionnaire (12-item version) and the Munich Diagnostic Checklist for DSM-III-R. The Gomel region is one of the areas that was most severely affected by the Chernobyl nuclear diaster in 1986. In the studied population sample 64·8% had a GHQ-score above the threshold of 2. A DSM-III-R psychiatric disorder was present in 35·8%, with especially high rates for affective (16·5%) and anxiety disorders (12·6%). Dysthymia, general anxiety disorder, adjustment disorders and ‘not otherwise specified syndromes’ made up almost two-thirds of the observed morbidity (22·9%). A higher prevalence of mental health problems, both in terms of the GHQ and the DSM-III-R was observed among people who have been evacuated and in mothers with children under 18 years of age. These data indicate that the Chernobyl nuclear disaster may be partly responsible for the high prevalence of (milder) psychiatric disorders and psychological distress in the Gomel region, even 6 years after the event. Future studies comparing the data from Gomel region with an unexposed area will have to provide a more definite answer concerning the impact of this nuclear disaster on mental health.