BACKGROUND: Worksites are considered to be a key channel for the delivery of interventions to prevent cardiovascular disease. The aim of this study was to evaluate the effect on the blood cholesterol levels of an intervention program offered by an occupational health service. METHODS: The intervention group consisted of 95 employees and the reference group consisted of 74 employees, in all, 169 subjects, with a serum cholesterol > or = 5.2 mmol/l. Both groups completed a standardized questionnaire. Occupational health nurses carried out the blood sampling before and after the program. The intervention group was then offered counseling on physical activity and a dietician offered individual counseling on healthy food habits. The reference group was not the subject of the intervention program. RESULTS: The mean cholesterol level decreased by 0.3 mmol/l (5%) in the intervention group and for the men the decrease was 0.5 mmol/l, while the mean level of the reference group was unchanged. Furthermore, there was a nonsignificant decrease of the mean triglyceride level in the intervention group. CONCLUSION: The results of this controlled trial indicates that risk factors for cardiovascular disease can be reduced by interventions at the worksite. Even modest reductions of cholesterol levels may reduce the risk to a tangible degree.