['The aim was to assess the effect of population-based mammography screening on treatment costs for fatal breast cancer in Turku, Finland.', 'The study included 556 women with invasive breast cancer, diagnosed at the age of 40-74 years in 1987-1993: 427 in the screened group (screen-detected or interval cancer) and 129 in the unscreened group (not yet invited or refused screening). Both groups were followed up for 8 years from diagnosis.', 'In the unscreened group, 32 (25%) patients died of breast cancer versus 49 (12%) in the screened group (p < 0.001). The non-discounted mean treatment costs were 2.8-fold for those dying of breast cancer compared to survivors: 26,222 euros versus 9,434 euros; the difference between means was 16,788 euros (95% CI 14,915-18,660) (p<0.001). The mean costs for fatal cases were high, irrespective of the way cancer was detected: 23,800 euros in the unscreened group versus 27,803 euros in the screened group; the difference between means was -4,003 euros (-10,810 to 2802) (p=0.245). In the unscreened group, patients with fatal breast cancer accounted for 41% (0.76/1.87 million euros) of the total treatment costs versus 29% (1.36/4.76 million euros) in the screened group. It was estimated that about one third of costs for fatal breast cancer were avoided through mammography screening, accounting for 72-81% of the estimated total treatment cost savings achieved by screening. About 31-35% of the screening costs for 1987 to 1993 were offset by savings in treatment costs.'] Does population-based mammography screening result in substantial savings in treatment costs for fatal breast cancer?