OBJECTIVES: To evaluate a population outreach program to promote screening for colorectal cancer (CRC) among average-risk insured men and women. STUDY DESIGN: In 2008, 58,440 Kaiser Permanente Colorado members unscreened for CRC received an interactive voice response (IVR) call followed by mailed fecal immunochemical test (FIT), or colonoscopy if requested. We used a quasi-experimental design with staged implementation, in which a random subset of eligible members was selected each week to receive the intervention. This design allowed the entire group to ultimately receive the intervention. METHODS: Survival models summarized time-specific comparisons of screening behaviors for members who received immediate outreach compared with those who had not yet received it. RESULTS: A total of 26,003 (45%) of the unscreened population completed screening, predominately due to the mailed kits. The unadjusted hazard ratio (HR) for the outreach effect on screening completion was 4.08 (95% confidence interval: 3.93-4.25) and adjusted HR was 3.75 (3.60-3.91). Lower levels of screening were seen in African Americans (HR 0.83; 0.77-0.90) and Hispanics (HR 0.84; 0.80-0.88) compared with whites, and in smokers (HR 0.77; 0.74-0.80) compared with nonsmokers. The outreach had greater impact among those without a primary care (HR 4.5 vs 3.0, P <.0001) or specialty care (HR 5.2 vs 3.5, P <.0001) visit compared with those with 1 or more visits. CONCLUSIONS: The rate of colorectal cancer screening in members after mailed FIT with IVR was almost 4 times higher than usual care, particularly in those without an office visit. Targeted approaches are needed for groups at risk for not screening.