Abstract Background To investigate colorectal cancer (CRC) screening rates by the faecal immunochemical test (FIT) according to sociodemographic characteristics and nationality. Methods Men and women, aged 56–74, invited to participate in the Flemish CRC screening programme in 2013 and 2014 were included in this study. We analysed the association between CRC screening uptake and sex, age, (first and current) nationality and several proxies for socio-economic status (SES). The statistical analysis was based on descriptive analyses and logistic regression models. Results A total of 1 184 426 persons were included in our analysis. The overall screening uptake was 52.3%, uptake varied by sex, age, nationality and SES. Lower participation rates were associated with the youngest and oldest age categories (56–60 and 70–74) and being male. All nationalities other than Belgian or Dutch were significantly less screened. Lower uptake of screening was also associated with several proxy’s for low SES, such as having an allowance for being disabled, not being able to work, being an extended minor and having a social allowance/minimum wage. The descriptive analysis showed a 27% difference in CRC screening uptake between the (early) retired and the people entitled to a minimum wage. Conclusions There is a significant difference between screening uptake and demographic and socio-economic variables in the first 2 years of the population-based screening programme in Flanders. Based on the study results, implementing strategies to improve participation in those subgroups is needed.