The influence of age on survival was studied in an unselected series of 31,594 females with breast cancer reported to The Cancer Registry of Norway during 1955-1980. The prognosis was best in patients aged 35 to 49 years, and poorest in the older (greater than or equal to 75 years) and the younger patients (less than or equal to 34 years). These trends were present in all stages and periods of diagnosis. The poor outcome among the older patients may, in part, be related to less aggressive treatment, while differences in treatment procedures hardly explain the poor prognosis among the younger patients.