Optimal adherence to combination antiretroviral therapy is essential to the health of older people living with HIV (PLWH), however, the literature on adherence and aging is limited. Using Medicaid data from 29 states (N = 5177), we explored correlates of optimal adherence among older PLWH. The prevalence of optimal adherence was low (32 %) in this study. Males were more adherent than females (APR = 1.11, 95 % CI 1.02–1.21, P = 0.0127); persons with three or more co-morbidities (APR = 0.67, 95 % CI 0.60–0.74, P < 0.001), two co-morbidities (APR = 0.86, 95 % CI 0.75–0.98, P = 0.0319) and one co-morbidity (APR = 0.82, 95 % CI 0.73–0.92, P = 0.0008) were less adherent than those without any co-morbidity; and residents of rural areas (APR = 0.90, 95 % CI 0.63–0.98, P = 0.0385) and small metropolitan areas (APR = 0.82, 95 % CI 0.72–0.94, P = 0.0032) were less adherent than residents of large metropolitan areas. There were no racial differences in optimal adherence. Targeted interventions that provide adherence support, case management, and peer navigation services may be of benefit in achieving optimal adherence in this population.