Lumpectomy with axillary dissection followed by radiotherapy is a frequently utilized technique for the treatment of selected breast carcinomas. Following this procedure, patients often present within a variable period of time with either clinical or mammographic abnormalities at the lumpectomy site suggesting recurrent cancer. In order to evaluate the utility of fine needle aspiration biopsy (FNAB) in the follow-up of such patients, aspirates were obtained 1-73 months after lumpectomy from 72 patients. A spectrum of cytologic changes was seen as a consequence of surgery and irradiation at the site of the lumpectomy as well as in the axilla and lumpectomy scar. The majority of these changes (94%) were benign and generally resolved during follow-up visits. Recurrent malignancy was detected in 4 of 72 patients. These results show that FNAB can reliably differentiate benign from neoplastic changes in postlumpectomy patients and indicate that FNAB may play an important role in the nonsurgical management of clinically alarming but benign postlumpectomy lesions.