The study was carried out to assess the short- and long-term effects of a Finnish Social Insurance Institution (SII) weight reduction programme in overweight primary health care clients and the suitability of the programme for use in health centres. The treatment group consisted of 22 men and 71 women, mean body mass index (BMI) 34.3, divided into 8 subgroups. These subjects participated in a 6-week weight reduction course led by public health nurses. Afterwards, there were six follow-up sessions and weight measurements at about 2-month intervals. A control group of 20 men and 76 women, mean BMI 33.5, received no weight reduction instruction during the 1 year that they served as controls. The weights, serum and high-density lipoprotein (HDL) cholesterol levels as well as blood pressures of the subjects in both groups were measured at entry to the study and at the end of the 1-year period. At that time the treatment group showed a weight reduction of 10.9 kg in men and 5.4 kg in women. The control group showed a mean weight gain of 0.9 kg in men and 0.2 kg in women. HDL cholesterol increased in the treatment group. The blood pressure decreased significantly in the category of subjects with a weight loss exceeding 4 kg weight. At the end of the 7-year follow-up period the mean weight reduction in the treatment group was 8.7 kg in men and 3.5 kg in women. Of men 53% and of women 21% still weighed over 10 kg less than at baseline. Both the clients and public health nurses found the weight reduction programme useful and applicable to health centres, preferably with extended time. The programme has now been adopted nationwide in the Finnish primary health care system.