OBJECTIVES: To evaluate the effect of a dietary treatment programme on blood cholesterol concentration in hypercholesterolaemic patients in general practice and to analyse subjectively experienced side-effects. DESIGN: A 1-year parallel trial comparing a new treatment programme with conventional treatment. SETTING: General practitioners in Roskilde county, Denmark. SUBJECTS: 355 men and women, aged 20-60 years, with a persistent blood cholesterol concentration above age- and gender-specific cut-off points (265 in an intervention group and 90 in a control group). INTERVENTION: A treatment strategy based on collaboration between doctor and dietitian using individual dietary advice and feedback from measured biological parameters. MAIN OUTCOME MEASURES: Serum lipids, body weight, blood pressure, dietary behaviour, health parameters, quality of life parameters and acceptance by patients and general practitioners. RESULTS: Total blood cholesterol concentration decreased by 14% (1.07 mmol l(-1), P 30) reduced body weight by 6% (P 110 mmHg, respectively. Risk score decreased and self-assessed health, physical and psychological well-being improved. CONCLUSIONS: The treatment strategy tested proved to be efficient, without side-effects and well accepted by patients and general practitioners. The results strongly suggest that hypercholesterolaemia can efficiently be treated non-pharmacologically in general practice.