BACKGROUND Dietary treatment of hypercholesterolemia is one of the most frequently proposed measures to prevent cardiovascular disease. In this study cost-effectiveness of dietary treatment in Spain was assessed. METHODS Cost-effectiveness ratio was measured in terms of cost per life years gained, comparing net programme cost to its effectiveness. Effectiveness was estimated using a model that incorporates the Framingham multiple logistic equation to obtain the number of coronary events prevented and life years gained according to age, sex and initial cholesterol concentration. In this study it was assumed that dietary treatment could reduce cholesterol concentration by 5% in the group of participants. Net programme cost was estimated as total programme cost less averted cardiovascular disease treatment costs due to disease prevention. Costs and benefits were estimated for 1990 using a 5% discount rate. RESULTS Cost per life year gained ranged from $6,270 to 61,439 in men and $28,067 to 171,459 in women, according to age and initial cholesterol concentration. The lowest cost-effectiveness ratio was obtained in individuals with a cholesterol concentration of 9.7 mmol/l (380 mg/dl) aged 45-49 years in men and 50-54 years in women, and the highest one was obtained in those men and women with a cholesterol concentration of 5.7 mmol/l (220 mg/dl) aged 60-65 years. Cost per life year gained was lower than $25,000 in men aged 35 to 64 years with a cholesterol concentration higher than 6.2 mmol/l (240 mg/dl) and it was lower than $35,000 in women aged 35 to 64 years with a cholesterol concentration higher than 9.3 mmol/l (360 mg/dl). CONCLUSIONS Individual dietary treatment of hypercholesterolemia could be considered an efficient use of health resources. Programme for dietary treatment of hypercholesterolemia should be recommended in men aged 35-64 years with hypercholesterolemia (> 6.2 mmol/l) and in women aged 35-64 years with very high cholesterol concentrations.