89 patients, who underwent conservative surgery for breast cancer were followed up with mammography and real-time sonography. 78 patients underwent postoperative irradiation. Depending on the time interval between irradiation and examination various alterations in mammographic and sonographic patterns were evident. Of 14 biopsy-confirmed local recurrences, 11 were diagnosed by mammography and 12 by sonography. Sonography was superior in the diagnosis of small recurrences in breasts with radiation-induced increased density, whereas mammography showed better results in the detection of tumours with microcalcifications. As a result of the different sonographic aspect of recurrent tumours and scar tissue, the number of false positive diagnoses of sonography was markedly lower compared to that of mammography (2 versus 18). Combined use of mammography and sonography should therefore lead to better results in the diagnosis of local recurrences and to a reduction of unnecessary biopsies.