Management of patients with mammary Paget's disease is controversial; recent recommendations range from primary radiotherapy to modified radical mastectomy. This review correlates associated breast findings with disease stage and outcome to help guide evaluation and treatment.Retrospective review of clinical, mammographic and pathologic data from 38 women with mammary Paget's disease treated between 1979 and 1995 was performed. Mastectomies were performed on all but two patients with the entire breast and lymph nodes evaluated for histopathologic evidence of carcinoma.Underlying carcinoma (ductal carcinoma in situ and/or invasive ductal cancer) was found in most patients (92%) even when no palpable mass was evident (85%); this carcinoma is often multifocal (73%). Mammography fails to identify the underlying disease in many patients with no palpable mass and multifocal underlying disease (64%). Patients with Paget's disease and a palpable mass have a much greater incidence of invasive cancer, multifocal lesions, and positive lymph nodes, and have worse survival.Although some patients with Paget's disease might be well treated by breast conservation therapy, many patients have underlying multifocal carcinoma (including invasive cancer), which can be inapparent by examination and mammography. Selecting candidates with disease amenable to complete excision without mastectomy is problematic.