The crude mammary recurrence rate was studied in 5-year age intervals for 1,382 Stage I and II breast cancer patients treated by conservative surgery and radiation therapy and followed for a median of 11 years. Patients younger than 40 had a significantly higher local recurrence rate (41/210, 19%) than did older patients (106/1172, 9%). The majority of excess recurrences in the younger patients occurred early, with recurrence rates between 5 and 10 years being equal for the 2 age groups. A comparison of the clinical characteristics of the patient groups yielded no obvious explanation for the higher local recurrence rate in the younger patients, and 15-year cancer-specific survival was identical. Within the younger age group, recurrence rate was independent of clinical tumor size, and was unaffected by adjuvant treatment. Young patients with positive axillary nodes or negative hormone receptors appear to be at particularly high risk for mammary failure. Despite this apparent correlation with biologic aggressiveness, the 41 patients with mammary recurrence experienced long-term survival from time of primary treatment which was not significantly worse than that of patients not having had local recurrence. For 37 patients with operable mammary recurrence, the 10-year survival from time of salvage surgery was 64%.