Importance Colorectal cancer (CRC) screening saves lives, but participation rates are low among underserved populations. Knowledge on effective approaches for screening the underserved, including best test type to offer, is limited. Objective To determine (1) if organized mailed outreach boosts CRC screening compared with usual care and (2) if FIT is superior to colonoscopy outreach for CRC screening participation in an underserved population. Design, Setting, and Participants We identified uninsured patients, not up to date with CRC screening, age 54 to 64 years, served by the John Peter Smith Health Network, Fort Worth and Tarrant County, Texas, a safety net health system. Interventions Patients were assigned randomly to 1 of 3 groups. One groupwas assigned to fecal immunochemical test (FIT) outreach, consisting of mailed invitation to use and return an enclosed no-cost FIT (n = 1593). A secondwas assigned to colonoscopy outreach, consisting of mailed invitation to schedule a no-cost colonoscopy (n = 479). The third groupwas assigned to usual care, consisting of opportunistic primary care visit-based screening (n = 3898). In addition, FIT and colonoscopy outreach groups received telephone follow-up to promote test completion. Main Outcome Measures Screening participation in any CRC test within 1 year after randomization. RESULTS Mean patient age was 59 years; 64%of patients were women. The sample was 41% white, 24%black, 29% Hispanic, and 7%other race/ethnicity. Screening participation was significantly higher for both FIT (40.7%) and colonoscopy outreach (24.6%) than for usual care (12.1%) (P <.001 for both comparisons with usual care). Screening was significantly higher for FIT than for colonoscopy outreach (P <.001). In stratified analyses, screening was higher for FIT and colonoscopy outreach than for usual care, and higher for FIT than for colonoscopy outreach among whites, blacks, and Hispanics (P <.005 for all comparisons). Rates of CRC identification and advanced adenoma detection were 0.4%and 0.8%for FIT outreach, 0.4% and 1.3%for colonoscopy outreach, and 0.2%and 0.4%for usual care, respectively (P <.05 for colonoscopy vs usual care advanced adenoma comparison; P >.05 for all other comparisons). Eleven of 60 patients with abnormal FIT results did not complete colonoscopy. Conclusions and Revelance Among underserved patients whose CRC screening was not up to date, mailed outreach invitations resulted in markedly higher CRC screening compared with usual care. Outreach was more effective with FIT than with colonoscopy invitation.