Access to care varies by sex such that interactions with insurance status result in mixed patterns of preventive services utilization. We examined sex-specific effects of ACA Medicaid expansions on receipt of CRC screening. We used Behavioral Risk Factor Surveillance System data (2008-2016) for adults aged 50-64 years with household income ≤138% of federal poverty level to examine self-reported lifetime use of guideline-recommended CRC screening services overall and by screening modality. We employed difference-in-difference models comparing changes in CRC screening in 20 Medicaid expansion states before and after the ACA to changes in 18 states that did not expand Medicaid during our study period. We divided the expansion period into implementation (2014) and post-expansion (2016) periods to account for possible lagged effects. We observed time-varying effects of Medicaid expansion that revealed relative increases in CRC screening occurring during the post-expansion period. Heterogeneous effects by sex and by screening modality were also observed: there was a significant relative increase of 16.2 percentage points (95% CI [2.2, 30.2]; p-value = 0.023) in lifetime colonoscopy use among women in expansion states relative to non-expansion states in the post-expansion period. There were no significant effects of Medicaid expansion among men. Health insurance expansion had a lagged but significant effect on CRC screening among low-income non-elderly women in Medicaid expansion states, but no effect for men. The observed increase in CRC screening among women suggests that barriers to CRC screening may differ by sex, and tailored interventions to increase CRC screening improve outcomes.Copyright © 2020. Published by Elsevier Inc.