Oesophageal adenocarcinoma (OAC) is less common and develops at a later age in women compared with men. Endogenous oestrogen may therefore protect against OAC development. A cohort of women with breast cancer, a tumour commonly treated with oestrogen antagonists, was examined to identify the subsequent risk of developing OAC. Earlier studies have implicated radiotherapy in increasing oesophageal cancer (OC) risk among women with breast cancer. West Midlands Cancer Intelligence Unit data recording cancer diagnosis and treatment information was examined to identify patients with a first malignant primary breast cancer during 1977-2004. Patients were followed until diagnosis of a second primary cancer, death or end of the time period examined. Age-adjusted and period-adjusted standardized incidence ratios (SIR) were calculated as an estimate of relative risk for a second primary OC. Seventy-three thousand six hundred and thirteen women were eligible for the study, providing 486 679 person years at risk for analysis. One hundred and thirty-two second primary OCs were observed, compared with 121 expected (SIR 1.09; 95% confidence interval: 0.91-1.29). Radiotherapy treatment in 37 888 women did not affect the risk of a second primary OC (SIR 1.07; 95% confidence interval: 0.79-1.41). No difference was identified when examined by OC morphology.There was no association between breast cancer and a second primary OC. Radiotherapy that avoids deep irradiation in the treatment of breast cancer, local nodes or recurrence was not associated with an increased risk of developing a second primary OC.