BackgroundAdhering to clinical prescriptions is known to protect against the effects of uncontrolled hypertension and of acute and chronic cardiovascular diseases, including diabetes. Contextually, positive associations between self-care behaviors and psychological constructs, such as self-efficacy, are widely acknowledged in the literature. However, still little is known about the psychological factors underlying the patient’s self-efficacy. This study aimed to investigate the psychosocial and behavioral correlates of self-efficacy related to treatment adherence in older patients with comorbid hypertension and type 2 diabetes mellitus.Participants and procedureItalian and Polish patients (≥ 65 years; N = 180) consecutively responded to self-report questionnaires measuring psycho-social (i.e., beliefs about medicines, perceived physician’s communication effectiveness, medication-specific social sup-port, self-efficacy) and behavioral factors (i.e., pharmacological adherence, medications refill adherence, intentional non-adherence) related to treatment adherence. Between-group comparisons and regression analyses were performed.ResultsFisher’s least significant difference (LSD) test showed significant differences between the Italian and Polish groups in all questionnaires (p < .01) with the Italian patients reporting more satisfactory scores. Younger age (β = .08, p = .045), female gender (β = 1.03, p = .042), higher medication refills adherence (β = –.07, p = .024), lower intentional non-adherence (β = –.03, p = .009), positive beliefs about medications (β = .13, p < .001), better quality of communication with the physician (β = .09, p < .001), and stronger perceived medication-specific social support (β = .06, p = .001) were significantly associat-ed with self-efficacy related to treatment adherence.ConclusionsFuture research and interventions should leverage psychosocial and behavioral factors to address self-efficacy contributing to enhancing adherence to clinical prescriptions.