PURPOSE: Adherence to dietary guidelines and consumption of a high-quality diet are essential to rebuild strength and to decrease tumor recurrence and mortality in patients with colorectal cancer. We examined the associations of the diet quality of patients who have colorectal cancer with the characteristics of the patients and their families, the patient's perceived barriers to following the diet, and the family's attempts to change the diet. DESIGN: A cross-sectional study design was employed. Patients with colorectal cancer were recruited from National University Hospitals in South Korea. Enrolled patients were over 19 years old. Enrolled relatives served as the primary caregivers of the patients. METHODS: A total of 216 patients who had colorectal cancer and their family caregivers were enrolled. We assessed patients' diet quality, their perceived barriers to following the dietary plan, and family caregivers' attempts to improve diet quality. FINDINGS: Patients with colorectal cancer were less likely to have healthy eating habits if they perceived barriers to the recommended dietary plan, and more likely to have healthy eating habits if they had family caregivers who attempted to change their own dietary habits. CONCLUSIONS: Strategies that target patients' perceived barriers to following a healthy diet and that encourage family members to facilitate the adoption of a healthy diet can be integrated into the treatment plan of patients with colorectal cancer. CLINICAL RELEVANCE: The results can be used as evidence for promoting the notion that diet interventions for patients with colorectal cancer focus on the patient-family dyad, which support overall quality of care in oncology care hospitals.