OBJECTIVE: To describe a combined behavioural treatment program for obese men, the 'Gustaf' study, and to evaluate treatment success by the means of weight loss, drop-out analysis and changes in metabolic risk factors. SUBJECTS: Eighty-six men, aged 43+/-9y (mean+/-s.d.) and BMI 37.7+/-4.4 kg/m(2), from the waiting list of the outpatient clinic and men directly approaching the Obesity Unit. DESIGN: Combined, behavioural modification treatment, by the means of group sessions, for one hour every week over a two year period. MAIN OUTCOME MEASURES: Weight loss and changes in risk factors after completion of one and two years study and description of treatment success in the form of changes in metabolic risk factors. RESULTS: The one year drop-out rate was 22% and the cumulative rate after two years was 34%. Mean weight decreased significantly from start (121kg) to one year (114kg, P<0.001) and to two years (115kg, P<0.001) in completers. Several metabolic risk factors (waist and hip circumferences, systolic blood pressure, serum cholesterol and plasma insulin) remained significantly decreased after two years of treatment. The complete metabolic syndrome was diagnosed in five men at onset, but in no one after two years. There was no difference in change of metabolic risk factors after one year between the men who lost 8-12% of initial body weight and those who lost more. CONCLUSION: Sixty-six% (57/86) of the obese men who started in the 'Gustaf' program were still in the program after two years. In spite of the relatively modest weight loss, the men maintained a large proportion of this weight loss and also maintained their improved metabolic risk factor pattern.