Histopathology of mucinous carcinomas which are also named as gelatinous or colloidal carcinomas of the breast have different aspects. These types of cases whichhavenot been analysed up to date by our clinics were chosen as subject. In this study, 21 cases of mucinous carcinoma of the breast which had been detected in files of Pathology Department of Istanbul Medical Faculty, between 1979 and 1985 were analysed. In these cases, which were all women, the average age had been found to be 54.8 and the minumum and the maximum ages were 28 and 78 recpectively. Tumors were found to encounter mostly in the 6th and 8th decades. Tumors were in the left breast in 11 cases and right breast in 4 cases. Tumor localisation in the latter cases were as the following; two in upper lateral, one in lower medial and one in central. The size of the tumors which had been extracted totally varied between 0.3 and 5.9 cm. in diameter. Axillary metastasis had been found in only one of the three cases in which axillary material had been studied. These findings were compared with reference data and the results obtained were evaluated.