The aim of this study was to determine whether breast cancer in women under forty has a poorer prognosis as compared to cancers occurring in older premenopausal women. From January 74 to December 90, 658 premenopausal women underwent surgery as first treatment for operable breast cancer (invasive ca., first single breast primary cancer, no personal history of invasive cancer, no inflammatory sign, tumor size under 7 cm). One hundred and thirty-nine patients were under 40 years old. Adjuvant treatment was determined according to nodal status: axillary node positive patients received chemotherapy and/or hormonotherapy (ovarian suppression). Patients’ characteristics (T, N, histologic grade, hormone receptors) are equal in both groups under and above 40 years. Median follow-up is 10 years. Overall survival is not significantly different between women under and above 40 years of age. On the other hand, disease free survival is shorter for women under 40 (P = 0.01). This difference is not explained by a more intensive follow-up after treatment for younger patients and prompted us to intensify or to respect dose intensity. The aim of this study was to determine whether breast cancer in women under forty has a poorer prognosis as compared to cancers occurring in older premenopausal women. From January 74 to December 90, 658 premenopausal women underwent surgery as first treatment for operable breast cancer (invasive ca., first single breast primary cancer, no personal history of invasive cancer, no inflammatory sign, tumor size under 7 cm). One hundred and thirty-nine patients were under 40 years old. Adjuvant treatment was determined according to nodal status: axillary node positive patients received chemotherapy and/or hormonotherapy (ovarian suppression). Patients’ characteristics (T, N, histologic grade, hormone receptors) are equal in both groups under and above 40 years. Median follow-up is 10 years. Overall survival is not significantly different between women under and above 40 years of age. On the other hand, disease free survival is shorter for women under 40 (P = 0.01). This difference is not explained by a more intensive follow-up after treatment for younger patients and prompted us to intensify or to respect dose intensity.