To evaluate the incidence of a positive bone scan at presentation in women with primary breast cancer, 389 consecutive 99Tcm bone scans over a ten-year period (1978-87) were retrospectively and blindly reviewed by a single observer. The study comprised all women clinically staged I-III (UICC criteria) and irradiated with radical intent in the Professorial Unit of Radiotherapy at this institution. The initial scan was performed within six weeks of primary surgery, and was judged to show metastatic disease in only 24/389 (6%) overall. The incidence of a positive scan increased with stage from 2/80 (2.5%), and 9/226 (4%) to 13/83 (16%) for stages I, II, and III respectively. Pre-operative haemoglobin, serum alkaline phosphatase level, age, menstrual status and degree of nodal involvement were not significantly associated with the risk of a positive scan. Patients found to have a positive scan experienced a significantly shorter overall survival than those with a normal scan (p greater than 0.001). After a mean follow-up time of 46 months (range 3-120 months), 45/365 originally normal scans 15% had converted to an abnormal scan, and a further 32 patients developed radiological evidence of bone metastases.