Purpose <p>Adherence to oral chemotherapy remains a significant challenge in cancer care, potentially compromising treatment efficacy and patient outcomes. Emerging evidence suggests that patients’ perceptions of their illness may influence adherence behaviors. This study aimed to evaluate patients’ perceptions of their illness and examine their association with adherence to oral chemotherapy.</p> Methods <p>The descriptive and cross-sectional design study was conducted with 90 patients who received oral chemotherapy in the oncology polyclinic of a university hospital. “Personal Information Form,” “Illness Perception Scale,” and “Oral Chemotherapy Adherence Scale” were used to collect data. Descriptive statistics were used to summarize participant characteristics. Based on the distribution of variables (assessed via Kolmogorov–Smirnov/Shapiro–Wilk tests), appropriate parametric and non-parametric tests were used. Spearman’s rank-order correlation evaluated associations between illness perception components and adherence.</p> Results <p>The most common symptom experienced by the patients in the identity dimension was fatigue (88.9%). In the illness representation, the average score of the subscale of illness coherence (9.43 ± 2.25) was the lowest. Oral Chemotherapy Scale total score was 78.41 ± 6.57. Weak but statistically significant positive correlations were found between adherence and personal control (<i>r</i> = 0.293), treatment control (<i>r</i> = 0.294), and illness coherence (<i>r</i> = 0.259) (<i>p</i> &lt; 0.05).</p> Conclusion <p>While causality cannot be inferred due to the cross-sectional design, findings suggest that stronger perceived control and a better understanding of illness are associated with higher adherence to oral chemotherapy. These results highlight the importance of integrating psychosocial assessment and tailored education into supportive cancer care practices.</p>