PURPOSE: We aimed to determine whether insurance expansions implemented through the Affordable Care Act (ACA) were associated with changes in coverage status, disease stage, and treatment of younger adults with testicular germ cell tumors (GCT). MATERIALS AND METHODS: We identified men aged 18–64 diagnosed with testicular GCTs between 2010 and 2015 in the National Cancer Data Base. We defined time periods as: pre-ACA (2010–2013) and post-ACA (2014–2015) and used difference-in-differences (DID) modeling to examine associations between state Medicaid expansion status and changes in insurance, stage at diagnosis, and treatment. RESULTS: Following the ACA, the proportion of patients with any health insurance increased 3.7% (95% CI 3–4.5) in Medicaid expansion states and 3.0% (95% CI 1.5–4.5) in non-expansion states, mainly by gaining Medicaid and private insurance, respectively. The largest increases occurred in low-income patients, where Medicaid expansion was associated with an adjusted increase of 14.5 percentage points (95% CI 7.2–21.8) in Medicaid coverage following the ACA. We did not observe reductions in late-stage diagnoses during the observation period. Changes in the proportion of patients receiving chemotherapy or radiation for advanced-stage cancers were ongoing prior to the ACA and differed between expansion and non-expansion states, limiting assessment of ACA-related effects on individual treatments. CONCLUSIONS: Post-ACA, the proportion of newly diagnosed testicular cancer patients with health insurance increased, with the largest effects seen among lowest income individuals. Our findings that changes in practice preceded the ACA and differed by expansion status highlight the need for caution in assessing the legislation’s impact.