Mucinous carcinoma (MC) of the breast is a rare and special type of malignancy, with a substantial amount of extracellular mucin. We compared the clinicopathological features and the long-term survival of MC patients with those of invasive ductal carcinoma-no special type (IDC-NST) patients, and we examined prognostic factors of MC. A total of 116 patients with mucinous carcinoma and 3,258 patients with IDC-NST who underwent surgery at our hospital (1977-2008) were enrolled. The 10-year overall survival rate and breast cancer-specific survival rate (BSS) of the MC patients (88.3%, 93.7%) were both significantly higher than those of IDC-NST patients (81.6%, 85.0%) (p=0.015, p=0.005, respectively). A Cox regression analysis demonstrated that MC tended to be an independent prognostic factor (hazard ratio 0.44, p=0.098). The BSS of the MC patients with positive lymph node (LN) metastasis was significantly poorer than that of the patients without it, by univariate analysis (p=0.002). The tumor size in the MC patients with positive LN metastasis (mean 3.2 cm) was significantly larger than that in the patients without it (mean 1.9 cm) (p=0.0004). Although a Cox regression analysis revealed no independent factor, MC patients with positive LN metastasis should be treated for advanced invasive ductal breast cancer.