A series of 82 consecutive cases of mucinous carcinomas of the female breast was investigated for their clinical, morphological, and histochemical features and for the influence of some tumor characteristics on its prognosis. Two groups, a "pure" subtype (n = 58) and a "mixed" subtype (n = 24), were considered, according to the absence or the presence of concomitant areas with typical infiltrating ductal carcinoma. Eighty patients were followed with an average of 7.4 years. The actuarial survival was 58.5% at 10 years. The group of pure mucinous carcinomas showed a statistically significant better prognosis (P = 0.0007) than that of the group of mixed tumors, as well as a lower percentage of axillary nodal metastasis. Tumor dimension of both pure and mixed mucinous carcinomas influenced the prognosis, since patients with T1 tumors had longer survival than those with T2 tumors (P = 0.05) and the latter showed less mortality than T3 tumor cases (P = 0.036). Node-negative patients also had a more favorable outcome with lower mortality than node positive patients (P = 0.007). None of the T1 pure mucinous carcinomas had axillary metastasis, which may have implications for the surgical protocols. The evaluation of quantitative and qualitative content in mucosubstances did not correlate with the prognosis. However, sulfomucins were demonstrated in 30.5% of cases; this fact points to add breast carcinoma to the group of neoplasms that may present as a metastatic sulfomucin-producing adenocarcinoma.