During a review of 67 cases of mastitis, 34 were diagnosed as cases of tuberculous mastitis. The majority of the patients with tuberculous mastitis were Black women. The mean age of the patients was 34 years. One patient was lactating and several were of postmenopausal age. All presented with unilateral breast masses, thought to be inflammatory in 10 and neoplastic in 10. In none was tuberculosis suspected clinically. The diagnosis of tuberculosis was based on the histopathological demonstration of tubercles, caseation and a granulomatous inflammation, with acid-fast bacilli in 5 instances. The differential diagnoses included duct ectasia, a foreign-body giant-cell reaction with fat necrosis, foreign material or an abscess, granulomatous mastitis, fungal mastitis, sarcoidosis and a syphilitic gumma.