Effects of dietary intervention on dietary habits and nutrient levels were studied in 240 women aged 50-65 years who had been operated for a stage I-II breast cancer. Following surgery the women who had participated in a dietary history interview were randomly assigned to one of two groups. The intervention group (n = 121) received individual dietary counselling aimed at reducing dietary fat intake to 20-25 per cent of energy (E per cent) while increasing intake of carbohydrates. No dietary advice was given to women assigned to the control group (n = 119). There was no significant difference between the groups in terms of base-line nutrient intake except for a higher energy intake in the control group (P less than 0.05). Sixty-three (52 per cent) of the women in the intervention group and 106 (89 per cent) of the women in the control group completed the 2-year follow-up. Energy intake decreased after 2 years in both groups and the difference between the groups remained (P less than 0.01). Total fat intake decreased in the intervention group by 12.9-23.3 E per cent after 2 years and by 3.1 E per cent in the control group. The intake of carbohydrates increased from 46.2 to 57.2 E per cent in the intervention group and from 46.2 to 48.9 E per cent in the control group. The study shows that dietary habits and intake of nutrients can be altered through dietary counselling to breast cancer patients, and that such changes are long lasting.