An attempt was made to undertake a randomized clinical trial of weight reduction in obese postmenopausal breast cancer patients as an adjuvant to primary surgical and radiotherapeutic treatment. The rationale was to improve prognosis which has been shown to be worse in the obese (probably because of its effect on extra-ovarian oestrogen production). Difficulties in recruiting a sufficient number of patients and the introduction of tamoxifen as anti-oestrogenic adjuvant therapy led to the decision to modify the aim of the study by limiting it to a feasibility study in 102 patients. In three hospitals in The Netherlands and in two hospitals in Poznan, Poland these patients were randomized in intervention and control groups according to a 3:2 ratio. Weight reduction in the intervention group was achieved by dietary means, ie caloric restriction was adapted to personal needs and behaviour of the patients. After 1 year a median weight loss of 6 kg was reached in both countries. In the Netherlands further follow-up indicated that this result could be maintained for another 2 years.