Purpose: This study evaluates the impact of Medicaid expansion under the Affordable Care Act (ACA) on melanoma staging at diagnosis, treatment utilization, and 3-year mortality outcomes. The objective is to determine whether Medicaid expansion led to earlier melanoma diagnosis and improved survival rates among non-elderly adults (ages 40-64) by analyzing data from the National Cancer Database (NCDB). Methods: A total of 12,667 patients, aged 40-64, diagnosed with melanoma from 2010 to 2020 were identified using the NCDB. Difference-in-difference (DID) analysis was performed to analyze tumor staging at presentation between Medicaid expansion states and non-Medicaid expansion states both prior to the expansion and after the expansion. Results: Of the total patients 2,307 were from the pre-expansion time period residing in Medicaid Expansion states (MES) and 1,804 in non-Medicaid expansion states. In the post-expansion time period there were 5,571 residing in the MES and 2,985 in the non-MES. DID analysis revealed a decrease in stage IV melanoma at diagnosis (DID -0.222, p <0.001) between MES and non-MES before and after Medicaid expansion. After expansion, in stage IV, the occurrence of primary surgery was 0.42 in non-MES and 0.44 (difference 0.02), DID analysis was not statistically significant. The use of immunotherapy in MES was significantly higher than non-MES after expansion (p<0.001), although DID analysis did not reveal a statistically significant difference. DID analysis showed a statistically significant decrease in 3-year mortality (DID -0.05, p=0.001) between MES and non-MES before and after Medicaid expansion. Conclusions: This study revealed the positive impact of the ACA’s Medicaid expansion on melanoma stage at presentation showing improved access to healthcare services can facilitate the diagnosis of early-stage melanoma and decrease mortality rate.