A historical prospective study was conducted at the Mercy Hospital of Pittsburgh, Pennsylvania (USA), to study the role of post-menopausal obesity in the recurrence and survival of breast cancer. Records from 301 post-menopausal women diagnosed with breast cancer from 1977 to 1985 were followed for at]east 5 years from data supplied by the Tumor Registry and medical records. Data collected included age, height, weight, race, hormone receptor status, stage and size of tumour, number of positive nodes, site of distant metastasis, first course of treatment, and 5 year recurrence and survival. Forty-five per cent of patients were obese (n = 136), while 55% were non-obese (n = 165). Obesity was defined by the Quetelet index (patients with values >27 were considered obese). The recurrence rates for the obese and non-obese groups were 40% and 39% respectively, and were not significantly different. Univariate and multivariate analyses showed that there was no significant association between obesity in post-menopausal women and likelihood of recurrence of or death from breast cancer.