In a population-based study, causes of death were traced of 418 deceased breast cancer patients diagnosed in 1960-1979 who survived at least 10 years after diagnosis. The pattern of causes of death in these patients was compared with the general female population using standardized mortality ratios (SMRs). Of 418 patients surviving at least 10 years, 196 (47%) died from breast cancer and 50 (12%) died from another cancer. The SMR for breast cancer was 15.8 (95% CI: 13.1-18.8) 10-14 years after diagnosis; it was still 4.7 (95% CI: 2.6-7.8) after 20 years. Overall mortality was higher than expected 10-14 years after diagnosis (SMR: 1.3; 95% CI: 1.1-1.5), but lower after more than 20 years (SMR: 0.6; 95% CI: 0.4-0.7). Despite a normal (or even improved) life expectancy for breast cancer patients 20 years after diagnosis the risk of dying from this disease remained elevated.