Abstract Objective Few studies use longitudinal data to identify predictors of colorectal cancer screening (CRCS). We examined predictors of (1) initial CRCS during the first year of a randomized trial, and (2) repeat CRCS during the second year of the trial among those that completed FOBT in Year 1. Methods The sample comprised 1247 participants of the Systems of Support to Increase Colorectal Cancer Screening (SOS) Trial (Group Health Cooperative, August 2008 to November 2011). Potential predictors of CRCS were identified with logistic regression and included sociodemographics, health history, and validated scales of psychosocial constructs. Results Prior CRCS (OR 2.64, 95% CI 1.99–3.52) and intervention group (Automated: OR 2.06 95% CI 1.43–2.95; Assisted: OR 4.03, 95% CI 2.69–6.03; Navigated: OR 5.64, 95% CI 3.74–8.49) were predictors of CRCS completion at Year 1. For repeat CRCS at Year 2, prior CRCS at baseline (OR 1.97, 95% CI 1.25–3.11), intervention group (Automated: OR 9.27, 95% CI 4.56–18.82; Assisted: OR 11.17, 95% CI 5.44–22.94; Navigated: OR 13.10, 95% CI 6.33–27.08), and self-efficacy (OR 1.32, 95% CI 1.00–1.73) were significant predictors. Conclusion Self-efficacy and prior CRCS are important predictors of future screening behavior. CRCS completion increased when access barriers were removed through interventions.