To compare breast cancer cumulative incidence, time evolution and stage at diagnosis between participants and non-participant women in a population-based screening program. Cohort study of breast cancer incidence in relation to participation in a population screening program. The study population included women from the target population of the screening program. The source of information for diagnostics and stages was the population-based cancer registry. The analysis period was 1999-2010. The Relative Risk for invasive, in situ, and total cancers diagnosed in participant women compared with non-participants were respectively 1.16 (0.94-1.43), 2.98 (1.16-7.62) and 1.22 (0.99-1.49). The Relative Risk for participants versus non-participants was 2.47 (1.55-3.96) for diagnosis at stagei, 2.58 (1.67-3.99) for T1 and 2.11 (1.38-3.23) for negative lymph node involvement. The cumulative incidence trend had two joint points in both arms, with an Annual Percent of Change of 92.3 (81.6-103.5) between 1999-2001, 18.2 (16.1-20.3) between 2001-2005 and 5.9 (4.0-7.8) for the last period in participants arm, and 72.6 (58.5-87.9) between 1999-2001, 12.6 (7.9-17.4) between 2001-2005, and 8.6 (6.5-10.6) in the last period in the non-participant arm. Participating in the breast cancer screening program analyzed increased the in situ cumulative cancer incidence, but not the invasive and total incidence. Diagnoses were earlier in the participant arm.