Treatment advocacy (TA) programs, based in AIDS service organizations and clinics, aim to engage clients into care and support antiretroviral treatment (ART) adherence through client-centered counseling; advocate for patients with providers; and provide social service referrals. Systematic evaluations of TA are lacking. We conducted a non-randomized evaluation examining relationships of TA participation to adherence, care engagement, social services utilization, unmet needs, patient self-advocacy, and adherence self-efficacy among 121 HIV-positive clients (36 in TA, 85 not in TA; 87% male, 34% African American, 31% White, 19% Latino). In multivariate models, TA participants (vs. non-TA participants) showed higher electronically monitored [85.3% vs. 70.7% of doses taken; b(SE) = 13.16(5.55), p < .05] and self-reported [91.1% vs. 75.0%; b(SE) = 11.60(5.65), p < .05] adherence; utilized more social service programs [Ms = 5.2 vs. 3.4; b(SE) = 1.97(0.48), p < .0001]; and had fewer unmet social-service needs [Ms = 1.8 vs. 2.7; b(SE) = -1.06(0.48), p < .05]. Findings suggest the need for a randomized controlled trial of TA.