BACKGROUND: Breast enlargement in men is a common condition with advancing age. The main problem in this age group is to differentiate gynecomastia or benign enlargement from carcinoma.PATIENTS AND METHODS: Over a 14-year period, 60 patients greater than or equal to 40 years old were operated on for unilateral breast masses (11 carcinoma, 49 gynecomastia) at the University College Hospital, Galway, Ireland. The medical records of these patients were reviewed and data were collected from patients' charts and histopathology records.RESULTS: Patients with carcinoma delayed significantly longer before presentation than patients with gynecomastia, a median of 33 versus 3.4 months, respectively. A lump was the presenting complaint in patients with carcinoma unless the disease was advanced. Patients with gynecomastia were more likely to present with pain; and the majority of these patients described tenderness on clinical examination. A history of carcinoma (18% and 0%) or a family history of breast carcinoma (36% and 14%) was more common in the patients with carcinoma than in those with gynecomastia, respectively (P <0.05; P = NS, respectively). Histories of consuming alcohol and smoking cigarettes were more common in those with gynecomastia (67% and 43%) than in those with carcinoma (55% and 18%). A similar proportion of patients in both groups were taking drugs known or suspected to cause gynecomastia (29% and 27%).CONCLUSIONS: Carcinoma must be excluded in patients presenting with unilateral breast masses, particularly in those patients who present with painless masses. Clues to the diagnosis are provided by a history of carcinoma or a family history of breast carcinoma. A history of consumption of drugs known to cause gynecomastia should not influence the decision to perform a biopsy on unilateral breast masses in older men.