We analyzed breast cancer subtypes using Korean Breast Cancer Society Registration Program data to compare clinical features and prognosis for triple-negative breast cancer (TNBC). A cohort of 26,767 breast cancer patients were divided in four groups: luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+ HER2+), HER2+ (ER-, PR-, HER2+), and triple-negative (ER-, PR-, HER2-). Clinicopathologic factors were evaluated. The luminal A (14,437 patients, 53.9%) subtype was the largest in our study. Compared with luminal A subtype, TNBC correlated with younger age, more aggressive characteristics and poor overall survival and breast cancer-specific survival. The hazard rate showed a peak at 24 months for the TNBC subtype, but after 60 months, risk was similar to that of the luminal A subtype. Higher T, N stage and histologic grade, and lymphatic and vascular invasion showed poor prognosis in TNBC patients, but on multivariate analysis only histologic grade and ki-67 status were related. Young age was related to poor prognosis in the luminal A subtype, however, age was not related to prognosis in the TNBC subtype. Of the 5,586 TNBC patients, 282 patients (7.11%) expired within 3 years of diagnosis. T and N stage and grade were significantly associated with prognosis on multivariate analysis. TNBC subtype is characterized by younger age with poorer outcome. However, younger age is not related to prognosis, and mortality risk decreases to that of the luminal A subtype, which is known to have the best prognosis after a few years.