Background: The overall incidence of breast cancer in South Asian countries, including Nepal, is low compared to Western countries. However, the incidence of breast cancer among young women is relatively high. Breast cancer in such cases is characterized by a relatively unfavorable prognosis and unusual pathological features. The aim of this study was to investigate clinico-pathological and biological characteristics in younger breast cancer patients (<40 years) and compare these with their older counterparts. Materials and Methods: Nine hundred and forty four consecutive female breast cancer patients, admitted to the Department of Surgery, Tribhuvan University Teaching Hospital, Kathmandu, Nepal between November 1997 and October 2012, were retrospectively analyzed. Results: Out of the 944 female breast cancer patients, 263 (27.9%) were <40 years. The mean age was $34.6{pm}5.0$ years among younger patients compared to $54.1{pm}9.9$ for those ${geq}40$ years. The mean age at menarche was also significantly lower ($13.5{pm}1.5$ vs $14.2{pm}1.5$ years p=0.001) while the mean duration of symptoms was significantly longer (7.6 vs 6.5 months p=0.004). Family history of breast cancer was evident in 3.0% of the young women versus 0.3% in the older one. Mammography was performed less frequently in younger patients (59.7%), compared to older (74.4%), and was of diagnostic benefit in only 20% of younger patients compared to 85% of older ones. At diagnosis, the mean tumor diameter was significantly larger in young women ($5.0{pm}2.5$ vs $4.5{pm}2.4cm$, p=0.005). Axillary lymph nodes were positive in 73% of younger patients and 59% of older patients. In the younger group, the proportion of stage III or IV disease was higher (55.1% vs 47.1%, $p{leq}0.05$). The proportion of breast conserving surgery was higher in young patients (25.1% vs 8.7%) and a higher proportion of younger patients receive neoadjuvant chemotherapy (9.9% vs 2.8%). The most common histological type was ductal carcinoma (93.1% vs 86%). The proportion of histological grade II or III was higher in younger patients (55.9% vs 24.5%). Similarly, in the younger group, lymphatic and vascular invasion was more common (63.2% vs 34.3% and 39.8% vs 25.4%, respectively). Patients in the younger age group exhibited lower estrogen and/or progesterone receptor positivity (34.7% vs 49.8%). Although statistically not significant, the proportion of triple negative tumors in younger age group was higher (22.4% vs 13.6%). Conclusions: Breast cancer in young Nepalese women represents over one quarter of all female breast cancers, many being diagnosed at an advanced stage. Tumors in young women exhibit more aggressive biological features. Hence, breast cancer in young women is worth special attention for earlier detection.