A total of 307 breast neoplasms and tumour-like conditions were reviewed to assess the frequency with which bone and/or cartilage occurred. Of 90 fibroadenomas, 1 (1.1%) and 2 of 158 breast carcinomas (1.3%) contained bone, one benign mesenchymoma contained cartilage, and one benign "mixed" tumour (pleomorphic adenoma) displayed cartilage and bone. Twenty-two papillomas and 34 cases of gynaecomastia did not contain any cartilage or bone. This study confirms the impression that the occurrence of bone or cartilage in human breast neoplasms is rare. These lesions are briefly discussed with reference to the pertinent literature.