Primary colonoscopy and fecal immunochemical testing (FIT) are considered first tier tests for colorectal cancer (CRC) screening. Although colonoscopy is considered the most efficacious test, FIT may achieve higher participation rates. It is uncertain what the best strategy is for offering population-wide CRC screening.This was a multicenter randomized health services study performed within the framework of the Polish Colonoscopy Screening Program (PCSP) between January 2019 and March 2020 on screening-naïve individuals. Eligible candidates were randomly assigned in a 1:1:1 ratio to participate in one of three competing invitation strategies: (I. control) invitation to screening colonoscopy only; (II. sequential) invitation to primary colonoscopy, and invitation for FIT for initial non-responders; or (III. choice) invitation offering a choice of colonoscopy or FIT. The primary outcome was participation in CRC screening within 18 weeks after enrollment into the study. The secondary outcome was diagnostic yield for advanced neoplasia (AN).Overall, 12,452 individuals were randomized into three study groups. The participation rate in the control group (17.5%) was significantly lower compared to the sequential (25.8%) and choice strategy (26.5%) groups (p<0.001 for both comparisons). The colonoscopy rates for participants with positive FITs were 70.0% for the sequential group and 73.3% for the choice group, despite active call-recall efforts. In the intention to screen analysis, advanced neoplasia detection rates were comparable between the control (1.1%), sequential (1.0%) and choice groups (1.1%).Offering a combination of FIT and colonoscopy as a sequential or active choice strategy increases participation in CRC screening. Increased participation in strategies with FIT do not translate into higher detection of AN. ClinicalTrials.gov Identifier: NCT03790475.