ABSTRACT: The Affordable Care Act (ACA) eliminated cost-sharing for evidence-based preventive services in an effort to encourage use.To evaluate use of colorectal cancer (CRC) screening in a national population-based sample before and after implementation of the ACA.Repeated cross-sectional analysis of the Medical Expenditure Panel Survey (MEPS) between 2009 and 2012 comparing CRC screening rates before and after implementation of the ACA.Adults 50-64 with private health insurance and adults 65-75 with Medicare.Self-reported receipt of screening colonoscopy, sigmoidoscopy, or fecal occult blood test (FOBT) within the past year among those eligible for screening.Our study included 8617 adults aged 50-64 and 3761 adults aged 65-75. MEPS response rates ranged from 58 to 63%. Among adults aged 50-64, 18.9-20.9% received a colonoscopy in the survey year, 0.59-2.1% received a sigmoidoscopy, and 7.9-10.4% received an FOBT. For adults aged 65-75, 23.6-27.7% received a colonoscopy, 1.3-3.2% a sigmoidoscopy, and 13.5-16.4% an FOBT. In adjusted analyses, among participants aged 50-64, there was no increase in yearly rates of colonoscopy (-0.28 percentage points, 95% CI -2.3 to 1.7, p?=?0.78), sigmoidoscopy (-1.1%, 95% CI -1.7 to -0.46, p?=?<0.001), or FOBT (-1.6%, 95% CI -3.2 to -0.03, p?=?0.046) post-ACA. For those aged 65-75, rates of colonoscopy (+2.3%, 95% CI -1.4 to 6.0, p?=?0.22), sigmoidoscopy (+0.34%, 95% CI 0.88 to 1.6, p?=?0.58) and FOBT (-0.65, 95% CI -4.1 to 2.8, p?=?0.72) did not increase. Among those aged 65-75 with Medicare and no additional insurance, the use of colonoscopy rose by 12.0% (95% CI 3.3 to 20.8, p?=?0.007). Among participants with Medicare living in poverty, colonoscopy use also increased (+5.7%, 95% CI 0.18 to 11.3, p?=?0.043).Eliminating cost-sharing for CRC screening has not resulted in changes in the use of CRC screening services for many Americans, although use may have increased in the post-ACA period among some Medicare beneficiaries.