Improving outcomes for people with HIV and mental illness will be critical to meeting the goals of the US National HIV/AIDS Strategy. In a retrospective analysis of the 2008-2010 cycles of the locally representative Philadelphia Medical Monitoring Project, we compared the proportions of HIV-infected adults with and without mental illness: (1) retained in care (≥2 primary HIV visits separated by ≥90 days in a 12-month period); (2) prescribed antiretroviral therapy (ART) at any point in a 12-month period; and (3) virally suppressed (HIV-1 RNA ≤200 copies/mL at the last measure in the 12-month period). Multivariable regression assessed associations between mental illness and the outcomes, adjusting for age, gender, race/ethnicity, insurance, alcohol abuse, injection drug use, CD4 count, and calendar year. Of 730 HIV-infected persons, representative of 9409 persons in care for HIV in Philadelphia, 49.0 % had mental illness. In adjusted analyses, there were no significant differences in retention (91.3 vs. 90.3 %; AOR 1.30, 95 % CI 0.63-2.56) and prescription of ART (83.2 vs. 88.7 %; AOR 0.79, 95 % CI 0.49-1.25) between those with and without mental illness. However, mentally ill patients were less likely to achieve viral suppression than those without mental illness (65.9 vs. 74.4 %; AOR 0.64, 95 % CI 0.46-0.90). These findings argue for the need to optimize ART adherence in this population.