The relationship of age with prognostic factors and outcome of breast cancer has long been controversial due to numerous confounding factors. In order to clarify the prognostic value of age, we analyzed a homogeneous population of 1,266 patients treated for breast cancer at the same institution (mean follow-up: 62 months). Three groups were compared: patients under 35 years of age, non-menopausal patients over 35 years of age, and post-menopausal patients under the age of 70 years. A higher frequency of undifferentiated tumors, histoprognostic grade-3 cancer, microscopic lymph-node involvement and negative hormonal receptor status was observed in patients under 35 years. In addition, clinical but not anatomical tumor size was greater in young patients, suggesting higher stromal activity. Metastasis-free survival and overall survival were significantly poorer before 35 years. Differences were observed when patients were matched with regard to stage, anatomic size, histoprognostic grade, microscopic lymph-node involvement and receptor status. Multivariate analysis of both overall and metastasis-free survival demonstrated that age younger than 35 years was an independent risk factor. Younger women had a higher risk of local recurrence but, unlike older women, they did not experience any worsening of the already unfavorable outcome due to recurrence. © 7995 Wiley-Liss, Inc.