Adherence to antiretroviral therapy (ART) results in HIV viral suppression, which is one of the main 90-90-90 targets. Little is known about the accuracy of provider and patient predictions of retention in care and adherence to ART. To address this gap, we conducted a longitudinal analysis of 100 HIV positive people newly eligible for ART initiation (based on the Russian guidelines of ART prescription) in St. Petersburg, Russia. We assessed the association between predictions prior to ART initiation by each patient or their primary HIV physician and treatment outcomes of ART retention and adherence assessed by review of pharmacy and laboratory data. We observed that physicians’ prediction was less accurate than ART outcomes compared to that of their patients. Providers should not rely on anticipated adherence and discuss openly the concerns about adherence with patients to identify those who need intervention to improve adherence.