The trend in the prognosis of female patients with breast cancer has been investigated by comparing Kaplan-Meier survival curves of different patient cohorts diagnosed during the period 1948-87. The study is based on 71,448 patients from the Danish Cancer Registry. The cohorts were defined by age at diagnosis, year of diagnosis and residential area. The survival time from diagnosis to death nearly doubled from 1948-57 to 1978-87 with the most important improvement taking place after 1978. Patients diagnosed in 1948-77 in the Copenhagen area had a far better prognosis than patients during this period in the rest of the country. For patients diagnosed in 1978-87 the prognosis, however, reached an equal level in all parts of the country. Thus, it is reasonable to assume that the national programme introduced in 1977 by the Danish Breast Cancer Cooperative Group (DBCG) has played an important role in these improvements.