Nearly perfect adherence to demanding antiretroviral therapy (ART) is now recognized as essential for HIV-positive patients to realize its life sustaining benefits. Despite the dire consequences of non-adherence, a large number of patients do not follow their ART regimen. While many factors influence adherence, the literature is dominated by studies on only one or a small set of them. Multivariate, theory-based models of adherence behavior are of great interest. The current study tested one such model, the Information, Motivation and Behavioral Skills (IMB) model of ART adherence (Fisher et al., under review). A sample of HIV-positive patients on ART in clinical care in Puerto Rico (N=200) provided data on adherence-related information, motivation and behavioral skills as well as adherence behavior per se. Structural equation model tests used to assess the propositions of the IMB model of ART adherence provided support for the interrelations between the elements proposed by the model and extended previous work. Implications for future research and intervention development are discussed.