This study aimed to determine the level of antiretroviral adherence and factors associated with adherence among patients receiving free antiretroviral therapy (ART) at one clinic in Tanzania. Adult patients were recruited into the cross-sectional study and completed a survey that included self-reported adherence over four days and over one month. Less than 95% adherence on either measure was considered "poor." Factors associated with adherence in unadjusted analyses (alpha = 0.10) were included in a logistic regression model. A total of 340 patients participated in the study, and 5.9% (20/340) reported poor adherence. The final model found poor adherence associated with: being young (odds ratio (OR) = 4.03) or old (OR = 6.68); having lower perceived quality of patient-provider interaction (OR = 2.75); and ever missing a clinic appointment (OR = 3.13). Results highlight good adherence, but suggest the importance of addressing: (1) age-specific challenges of adherence through counseling and support; (2) client-focused care and quality of patient-provider interaction; and (3) clinic appointment reminder systems.