OBJECTIVES. The aim of this study was to carry out a cost-effectiveness analysis of a multifactorial intervention programme in treated hypertensive patients. DESIGN. A cost-effectiveness analysis based on 3 years of follow-up in an open, randomized, parallel-group study with allocation either to a comprehensive, multiple-risk factor modification programme or to conventional treatment. SETTING. An outpatient clinic of a city hospital. SUBJECTS. Inclusion criteria were: male sex, age 50-72 (mean 66.4) years, treated hypertension and at least one of the following: serum cholesterol > or = 6.5 mmol L-1, and/or smoking and/or diabetes mellitus. A total of 508 patients were included in the study. INTERVENTIONS. Advice given to individuals, and group meetings based on nutritional advice and behavioural treatment principles. If necessary, drug therapy could be instituted to achieve the treatment goals in the intervention group: serum total cholesterol of