A study was carried out to assess the factors predisposing to chronic post-treatment pain in the breast area and in the ipsilateral arm in patients treated for breast cancer using two multivariate models. In the study 509 patients with non-metastasized breast cancer who were treated during 1988-1994 completed the questionnaire about pain in the operated breast and in the ipsilateral arm 10-58 months after surgery. The factors included in the analysis were: age, type of operation, size of the tumour, number of lymph nodes removed, involvement of lymph nodes, complications of surgery, intensity of the acute postoperative pain remembered by the patient, number of doses of analgesics, number of months from surgery, adjuvant radiotherapy, chemotherapy and endocrine treatment. The most important factors included in the models of chronic pain were: intensity of the acute postoperative pain, the type of operation, involvement of regional lymph nodes and radiotherapy.