The effect of age on outcome was analysed in an unselected series of 1730 breast carcinoma patients reported from Stockholm county to the Swedish Cancer Registry during 1961-1963. The follow-up time was 18 to 21 years. Patients aged less than 50 years at diagnosis fared better than those who were older (p less than 0.05) but the difference was only significant during the period 0-9 years (p less than 0.001). No significant differences in survival were observed between separate age groups when patients in a random sample consisting of 389 cases were divided by histopathologic axillary node status. The main cause of the demonstrated age effect thus seems to have been a more favourable tumour stage distribution among the young patients. It is concluded, however, that a comprehensive analysis of the effect of age on the outcome of breast carcinoma would require a more detailed stage grouping than, in practice, is available in an unselected series of patients from a whole country or region.