The objective of this study was to evaluate a medical outreach program that targets unstably housed human immunodeficiency virus (HIV)- infected individuals. One hundred sixty-one cross-sectional interviews were conducted prior to and after establishing a medical outreach program in single room occupancy hotels. Participants' mean age was 42 years; 58% were men, 95% minority, and 59% active substance users. The postintervention group was more likely to have a regular health care provider (p = 0.02), and take Pneumocystis carinii pneumonia prophylaxis (p = 0.03) and antiretroviral medication (p = 0.02) than the pre-intervention group. Quality of care was more positively perceived in the postintervention group (p = 0.001). On multivariate analysis the postintervention group remained more likely to have a regular provider (OR = 5.3, p = 0.02), take antiretroviral medication (OR = 5.7, p = 0.02), and have a better perception of quality of care (OR = 4.9, p = 0.003). A medical outreach program targeting unstably housed HIV-infected individuals was associated with increased use of regular medical care and improved perceived quality of care. (Authors)