To evaluate the feasibility of using a low-fat diet (i.e. 20-25% of energy (E%) as fat) as a component of adjuvant therapy for breast cancer patients, 240 females aged 50-65 years and operated for a stage I-II breast cancer were entered into a randomized study. The intervention group (n = 121) was to reduce dietary fat intake to 20-25 E% and to increase the intake of carbohydrates. Dietary counselling complemented other adjuvant treatments and the patients were followed for two years. No dietary advice was given to patients in the control group (n = 119). There was no significant difference between the groups in terms of base-line nutrient intake except for higher energy intake in the control group (p less than 0.05). Only 52% of the patients in the intervention group followed through with the dietary regimen for two years, and 89% of the patients in the control group had a two-year follow-up. Energy intake decreased in both groups after two years, and the difference between the two groups remained (p less than 0.01). Total fat intake decreased from 36.2 E% to 22.2 E% after one year in the intervention group and remained at that level after two years. Total fat intake in the control group decreased by 3.6 E% after two years. The low compliance raises concern about the protocol design. The study nevertheless indicates that a long-term reduction of dietary fat intake can be implemented in breast cancer patients.