Many older Americans do not receive needed care for mental health and substance use disorders (MHSUD), and there are substantial racial and ethnic disparities in receipt of this care across the lifespan. Medicare introduced cost-sharing parity for outpatient MHSUD care during the period 2010-14, reducing beneficiaries' out-of-pocket share of MHSUD spending from 50 percent to 20 percent. Among traditional Medicare beneficiaries ages sixty-five and older, we examined changes in MHSUD use and spending during the period 2008-18 for low-income beneficiaries with the cost-sharing reduction versus a control group of beneficiaries with free care throughout the study period among Black, Hispanic, Asian, and American Indian/Alaska Native versus White beneficiaries. Among older Medicare beneficiaries, overall use of MHSUD services increased during this period. For White beneficiaries, MHSUD cost-sharing parity was associated with an increased likelihood of having specialty MHSUD visits and medication use and a reduced likelihood of having unmonitored MHSUD medication use and MHSUD emergency department visits and hospitalizations. However, cost-sharing parity was associated with smaller or no gains in MHSUD services use for racial and ethnic minority beneficiaries compared with White beneficiaries, thus widening racial and ethnic disparities in MHSUD care.