Commercial insurance covers a follow-up colonoscopy (COL) after a positive colorectal cancer (CRC) screening test with no patient cost-sharing. Instituting a similar policy for Medicare beneficiaries may increase screening adherence and improve outcomes. The cost-effectiveness of stool-based CRC screening was compared across adherence scenarios that assumed Medicare coinsurance status quo (20% for follow-up COL) or waived coinsurance. The CRC-AIM model simulated previously unscreened eligible Medicare beneficiaries undergoing stool-based CRC screening at age 65 for 10 years. Medicare costs, CRC cases, CRC deaths, life-years gained (LYG), and quality adjusted life-years (QALYs) were estimated versus no screening. Scenario 1 (S1) assumed 20% coinsurance for follow-up COL. Scenario 2 (S2) assumed waived coinsurance without adherence changes. Scenarios 3-7 (S3-S7) assumed that waiving coinsurance increased real-world stool-based screening and/or follow-up COL adherence by 5% or 10%. Sensitivity analyses assumed 1%-4% increased adherence. Cost-effectiveness threshold was ≤$100,000/QALY. Waiving coinsurance without adherence changes (S2) did not affect outcomes versus S1. S3-S7 versus S1 over 10 years estimated up to 3.6 fewer CRC cases/1000 individuals, up to 2.1 fewer CRC deaths, up to 20.7 more LYG, and had comparable total costs per-patient (≤$6,478 vs $6,449, respectively) as reduced CRC medical costs offset increased screening and COL costs. In sensitivity analyses, any increase in adherence after waiving coinsurance was cost-effective and increased LYG. In simulated Medicare beneficiaries, waiving coinsurance for follow-up COL after a positive stool-based test improved outcomes and was cost-effective when assumed to modestly increase CRC screening and/or follow-up COL adherence.