Granulomatous mastitis is a rare inflammatory breast lesion, usually presented with rapidly enlarging palpable mass in young parous women and can simulate carcinoma. Unnecessary surgical procedure can be avoided if the nature of the lesion were defined by fine needle aspiratio(FNA) cytology. We experienced a case of bilateral granulomatous mastitis diagnosed by FNA cytology. The patients was a 31-year-old woman with one month history of a rapidly enlarging mass in the left breast. considered clinically to be malignant. After 4 years. she presented with a palpable mass in the right breast. The FNA cytology smears contained numerous aggregates of epithelioid histiocytes admixed with Langhans' and foreign body giant cells, lymphoytes, neutrophils and apoptotic debris leading to a diagnosis of granulomatous mastitis. The subsequent lumpectomy of the left breast confirmed the diagnosis of granulomatous mastitis. The FNA cytology smears from right breast showed identical cytologic findings.