Purpose: This study aims to determine the mediating role of trust in the physician in the effect of the physician’s open communication on patients’ adherence to treatment. Methods: This cross-sectional study included 594 patients who applied to a public hospital in Turkey for healthcare services. Participants completed scales for physicians’ open communication, trust in physicians, and treatment adherence. Data were analyzed using descriptive statistics, Pearson correlation, and structural equation modeling. SPSS and AMOS programs were used to analyze the research data. Results: Open communication of physicians was significantly associated with trust in physicians (r=0.752, p<0.01) and treatment adherence (r=0.612, p<0.01). Trust in physicians and treatment adherence were also significantly associated (r=0.671, p<0.01). Structural Equation Model and bootstrap analysis showed that trust in physicians fully mediated the relationship between open communication and treatment adherence (β=0.529; 95% confidence interval, 0.390–0.712). Conclusion This study found that open communication and trust increased patient adherence to treatment and confirmed that trust fully mediated adherence to treatment. Physicians’ open communication with patients increases patients’ trust in their physicians, thereby improving their treatment adherence. These findings demonstrate the importance of both physicians and medical students gaining competence beyond their technical competence to communicate effectively and build trust. In medical education, students should be given importance in acquiring behavioral skills.