Background . The importance of HIV viral suppression is widely known, however few studies have examined the effects of homelessness on HIV viral suppression. Methods . The study included HIV-seropositive patients in a health care for the homeless program (HCH). Electronic medical record data for 138 patients were analyzed to compare demographic characteristics, health characteristics, and utilization by housing status. For the 95 individuals with available HIV viral loads, multivariable logistic analysis was performed to examine factors associated with incomplete viral suppression. Results . The adjusted odds ratio of incomplete HIV viral load suppression was 3.84 times higher in homeless compared with housed (95% CI 1.36–10.36) individuals. Illicit drug use and combined antiretrovirals (cART) were associated with HIV viral suppression. Conclusions . Homelessness predicted incomplete HIV viral suppression. Stable housing may improve viral suppression and access to cART. Drug use was associated with viral suppression, likely because of patient engagement with on-site addiction services.