Marginalized populations are disproportionately affected by HIV, yet they have poor access to health services. Outreach programs focus on improving access, but few are evaluated. We assessed a medical outreach program targeting unstably housed, HIV-infected individuals. We extracted data from 2003-2005 to examine whether keeping medical appointments was associated with patient and program characteristics. Patients kept appointments more frequently when they were walk-in or same-day appointments (compared with future appointments; adjusted odds ratio [AOR]=1.69; 95% confidence interval [CI] = 1.38, 2.08), when they were at a community-based organization's drop-in center (compared with single-room occupancy hotels; AOR=2.50; 95% CI=1.54, 4.17), or when made by nonmedical providers (compared with medical providers; future appointments: AOR = 1.38; 95% CI = 1.05, 1.80; same-day appointments: AOR = 1.70; 95% CI = 1.03, 2.81). These findings demonstrate the importance of program-related characteristics in health services delivery to marginalized populations.