It is well recognized that a negative mammogram report does not exclude the presence of breast carcinoma. This study examines the accuracy of mammography in patients with palpable breast cancer. In particular, the study evaluates the reasons underlying negative mammography in breast cancer. All patients with Paget's disease, carcinoma in situ lesions or lesions infiltrating skin were excluded. A total of 291 patients presenting with palpable breast carcinoma underwent mammography prior to biopsy. False negative reports occurred in 16.5% (48). The sensitivity of mammography increased with age, from 70% (14/20) in 31-40-year-olds to 91% (113/124) in women over 60 years. Retrospective review of false negative mammograms showed that 30% of these were deemed normal while 20% were obvious oversights. The remaining 50% showed subtle radiographic abnormalities, consistent with but not diagnostic of malignancy.