For evaluation of clinical features and state of the art in the treatment of breast cancer in Iran, we studied 347 consecutive patients among 1123 hospital admissions (in 14 hospitals in three cities) who had undergone surgery for a mass in their breasts during a 2-year period, 1991 to 1992. Thirty-nine additional patients with breast cancer had been treated in the second year of the study, an increment of 8.9%. The relative frequency of positive biopsies for breast cancer was 31% for the entire series. In Teheran, Babol and Yazd, it was 35%, 24.2% and 18.1%, respectively. The mean age for the entire series was 48 +/- 1 years. The mean age for patients from Yazd was 51 +/- 9, which was higher than the mean age (41.5 +/- 16) of patients from Babol. The pathologic diameter was > 2.1 cm (pT2 and pT3) in 59.36% of the tumors. In 15.56% of the patients, the exact size of the tumor was not available. In 83.45% of the patients, the tumors were reported as infiltrating ductal carcinoma. Of 173 patients in whom regional nodes had been histologically examined, 80% had metastatic involvement (stage II disease). Modified radical mastectomy had been used more than radical mastectomy in this series, but the choice of the operation was not related to the size of tumor.