An important but understudied public health problem in HIV/AIDS research is disparities in highly active antiretroviral therapy (HAART) discontinuation among those with a comorbid serious mental illness (SMI). Despite evidence that Blacks are more likely to discontinue HAART than Whites, few studies have investigated disparities in HAART use and health outcomes among individuals with HIV/AIDS and a comorbid SMI. This study aimed to 1) assess the relationship of race and age on HAART discontinuation; 2) assess whether mental health visits mediate the relationship of race and age on HAART discontinuation; and 3) determine if HAART discontinuation is associated with hospitalizations for all-cause and immunocompromised conditions, and if this differs by race and age. HIV Research Network data from 2000-2010 were used for this study. The cohort was selected among individuals aged 18 or older, diagnosed with HIV/AIDS and a comorbid SMI, in care for HIV/AIDS, and initiated HAART between 2001-2007. The cohort was followed for four years to assess HAART discontinuity and treatment outcomes. Logistic regression was used to analyze the proposed relationships between race and age on HAART discontinuation, mental health visits, and hospitalizations for all-cause and immunocompromised conditions. HAART discontinuation was not statistically significantly different between Black and White individuals, but Hispanics had 32% lower odds than Whites of discontinuing HAART. Younger age was associated with a 28%-74% greater odds of HAART discontinuation compared to those aged 50 and older. Mental health visits did not differ significantly between Blacks and Whites, but Hispanics were more likely to have mental health visits than Whites. Ten or more mental health visits was a partial mediator between younger age and HAART discontinuation, with adults aged 18-29 and 30-39 years less likely to have 10 or more mental health visits and more likely to discontinue HAART. Compared to Whites, Blacks were more likely to be hospitalized in year four for all-cause and immunocompromised conditions. Individuals who discontinued HAART were less likely to have a year four all-cause hospitalization than those who continued HAART. This research deepens our understanding of disparities in HAART continuity and the impact on health outcomes for a vulnerable population.