Mammographic changes after lumpectomy, axillary dissection and irradiation are common and unpredictable. To study the significance of these changes at the first follow-up mammogram, we retrospectively reviewed reports of 172 women treated in this manner between 1979 and 1988. The mean follow-up time was 50 months. Eight patients had recurrences in the same breast, while 13 patients had carcinoma develop in the opposite breast. The mean time of follow-up mammograms was 11 months (range of one to 48 months). Twenty-six patients had a normal mammogram, while 146 patients had some changes within the irradiated breast. Thirty-one patients had suspicious findings--a mass, speculation or new microcalcifications. None of these 31 patients had carcinoma confirmed by biopsy or follow-up examination. Of eight patients with recurrence in the same breast, six had a biopsy because of findings on physical examination, while two had changes from previous mammograms. The mean time to recurrence was 50 months (range of 24 to 81 months). We conclude that mammographic changes in the irradiated breast are common after lumpectomy and irradiation for carcinoma of the breast. A baseline mammogram should be done six months after irradiation is completed. Changes that occur at this time should be considered secondary to surgical treatment and irradiation and are not an indication for immediate biopsy. These findings should be reconfirmed by a mammogram performed one year after irradiation to prove that these changes are stable. Physical examination and yearly mammography of both breasts are imperative in the follow-up evaluation of patients treated in this manner.