OBJECTIVES: This study aimed to evaluate changes in the rate of any reported disability days in young adults after the implementation of the dependent coverage provision under the Affordable Care Act (ACA) in September 2010. METHODS: A retrospective study was conducted by pooling data from the Medical Expenditure Panel Survey into two time periods: 2008 to 2009 and 2011 to 2012. Disability day was defined a day that individuals lost at least a half-day or more due to a physical illness, injury, a mental or emotional problem. A difference-in-difference approach was used to estimate the impact of the dependent coverage provision on any reported disability days between young adults aged 23 to 25 years and adults aged 27-29 years old. Covariates included race/ethnicity, family income, marital status, student status, and employment status. Person-level weight was used to account for the complex survey design. RESULTS: The data set included 8,013 total individuals with 4,026 young adults and 3,989 adults in control group. The unadjusted rate of any reported disability days before the implementation of the ACA was 45% in young adults and 49% in the control group. After the ACA, unadjusted rates reduced in both groups to 41% in young adults and 42% in the control group. The estimated change in the rate of any reported disability days was 2.38% (95% CI: -3.84% to 8.60%). CONCLUSIONS: Findings suggest that the extended dependent coverage under the ACA did not produce a greater reduction in young adults’ disability days in comparison to the control group. Disability days were lower for both groups after the implementation of the ACA’s dependent coverage provision. Future studies should examine the impact on the numbers of days lost due to a physical illness, injury, a mental or emotional problem.