Research examining variables that influence medication adherence among HIV-positive individuals remains an important priority. The patient-provider relationship may influence HIV medication adherence, though findings have varied across studies and there is a paucity of research examining mechanisms that may account for patient-provider influences on adherence. One potential mechanism that may explain this relationship is patient’s beliefs about medications, specifically how patients weigh the necessity of medications relative to concerns about negative side effects. Using data from a sample of 116 HIV patients recruited during outpatient care, this study aimed to (a) examine the effect of the patient-provider relationship on both adherence and intentional nonadherence; and (b) clarify whether there is an indirect effect of this relationship through medication beliefs. Primary study hypotheses were tested using bootstrapped mediation models. Results showed that the patient-provider relationship was positively associated with adherence but not intentional nonadherence. There was strong support for an indirect effect of this relationship through medication beliefs for adherence but not intentional nonadherence. This study could inform interventions to improve the patient-provider relationship as well as target potentially modifiable patient beliefs about their medications