The UK Trial of Early Detection of Breast Cancer (TEDBC) is a non-randomised study, which was set up in 1979 to investigate the effect of screening and education about breast self-examination on breast-cancer mortality. We report mortality results after 16 years of follow-up, including results by age at trial entry. Eight centres (two screening, two breast self-examination, and four comparison) in England and Scotland recruited women aged 45-64 years into the initial cohort, with women reaching age 45 years during the 7-year study period included in later cohorts. The observed number of deaths from breast cancer in each centre was compared with the expected number, which was calculated by Poisson regression model; expected numbers were adjusted for pretrial breast-cancer mortality. Results were analysed by 5-year age-groups, and for women aged 45-46 years and 47-49 years at entry. Breast-cancer mortality was 27% lower (rate ratio 0.73 [95% CI 0.63-0.84]), adjusted for pretrial rates, in cohort 1 in the two screening centres combined than in the comparison centres. No reduction in mortality in the two breast self-examination centres combined was seen (rate ratio 0.99 [0.87-1.12]). The mortality reduction in the screening centres did not differ significantly across age-groups; a 35% reduction was seen in women in all cohorts aged 45-46 years at entry (rate ratio 0.65 [0.50-0.86]). Results were similar when deaths were restricted to those in patients diagnosed within 10 years of trial entry. The results from TEDBC support those from randomised trials in Edinburgh and elsewhere, and show that a reduction in breast-cancer mortality resulting from screening can be achieved in the UK. There was no evidence of less benefit in women aged 45-46 years at the start of screening; the effect of screening in this age-group begins to emerge after 3-4 years.