The aim of the present study was to evaluate breast cancer risk in women aged 40–45 years not included in the routine mammographic screening programme in the Czech Republic and to assess the suitability of the screening interval. Our cohort study was conducted using registry data of one mammography centre (Bulovka Hospital in Prague) between 1 January 2008 and 31 December 2017. The risk of breast cancer was evaluated using a positive predictive finding (PPF) corresponding to the Breast Imaging-Reporting and Data System (BI-RADS) scores of 4 and 5. The annual PPF incidence rate achieved 2.25 per 1000 women aged 40–45 years and was not significantly different from that (3.31) of women of 45–50 years of age as demonstrated by an adjusted hazard ratio of 0.75 (95% confidence interval: 0.42–1.33). It was found that a screening interval longer than 3 years increased the chance of PPF occurrence 1.7 times independently of the women’s age, signalling a risk of failure of early detection of breast cancer. The same PPF incidence rates both in women aged 40–45 years and in older ones indicates that even younger women should be eligible for enrolment in the routine mammographic screening programme in the Czech Republic.