In order to evaluate the prognostic significance of risk factors for developing breast cancer, a population-based study was conducted of 2,445 breast cancer patients diagnosed in Denmark, 1983-1984. Data on clinical and pathological characteristics of breast cancer were derived from the Danish Breast Cancer Cooperative Group and data on risk factors from a self-administered questionnaire. Among 1,744 patients (71%) with complete information, survival was determined primarily by size of the tumour, skin invasion, number of positive lymph nodes and grade. No significant association was found between survival and reproductive or hormonal risk factors, dietary variables, alcohol consumption and smoking. Low current body weight and weight loss indicated a poor prognosis, independent of the clinical characteristics of the tumour.