Stage of disease at diagnosis is a predictor of breast cancer survival. We used data from the Danish Cancer Register and the Danish Breast Cancer Cooperative Group to study stage distribution in 0-69-year-old Danish breast cancer patients diagnosed in 1978-1994. We constructed a modified Nottingham Prognostic Index (NPI) calculated from the number of excised and positive lymph nodes, malignancy grade and tumour diameter. This NPI could be calculated for 63% of the patients, and among these the stage distribution improved during the study period. The proportion of patients with a poor prognostic score decreased from 27% to 20%. Based on a comparison of the crude 3-year survival of patients with an NPI score and those without, it seems probable that the stage of disease at diagnosis on average improved in Danish breast cancer patients below age 70 during the 1980s and the early 1990s.