There is growing evidence that early treatment with antiretroviral therapy (ART) confers benefit to HIV-infected persons and may reduce the risk of transmission. Among an urban poor sample living with HIV who meet guidelines for but are not taking ART, we explored treatment beliefs at baseline and subsequent ART uptake over the following 12 months. Most demographic/background characteristics did not differ between ART initiators and noninitiators, but baseline beliefs of expectancies about treatment ease, efficacy, and readiness sensitively predicted ART initiation. Treatment-related stigma/social concerns did not. Results offer direction for interventions to optimize treatment among those most in need.