Six patients with augmentation prostheses presented with a firm, painless, breast mass that could not be visualized by mammography. One lesion was demonstrated to be solid by ultrasound, and the remaining sonograms were nondiagnostic. The lesions were indistinguishable from carcinoma, by physical examination. All of the patients had fine needle aspiration biopsy despite close proximity to the implant. The patients all had silicone granulomas related to silicone leakage. Our experience suggests that fine needle aspiration biopsy is a useful technique to evaluate palpable breast masses that are not visualized by mammography in patients with augmentation prostheses.