Background: In our published randomized trial in colorectal cancer, group 1 (n = 37) received individualized nutritional counseling and education about regular foods, group 2 (n = 37) received dietary supplements and consumed their usual diet of regular foods, and group 3 (n = 37) consumed their usual diet of regular foods. Neither group 2 nor group 3 received individualized counseling. Early nutritional counseling during radiotherapy was highly effective at reducing acute radiotherapy toxicity and improving nutritional intake/status and quality of life (QoL). Efficacy persisted for 3 mo after the intervention. Objective: The objective was to perform long-term follow-up in survivors of that clinical trial to specifically evaluate survival, late toxicity, QoL, and nutritional variables. Design: Medical data were collected from patients' records, and pre-scheduled interviews were conducted by dietitians for individualized evaluations. Analyses and comparisons between groups (adjusted for stage) were performed after a median follow-up of 6.5 (range: 4.9-8.1) y. Results: Patients complied with the Radiotherapy Department's follow-up protocol. Nutritional deterioration was higher (P < 0.001) in group 3 (n = 26) and group 2 (n = 29) than in group 1 (n = 34). Adequate nutritional status was maintained in 91% of group 1 patients but not in any of the group 3 patients (P < 0.002). Intakes in group 1 were similar to reference values, and the patients adhered to the prescribed recommendations. Intakes in groups 2 and 3 were lower than recommended intakes: group 3 ≃ group 2 < group 1 (P = 0.001). Median survival in group 3 was 4.9 y (30% died), in group 2 was 6.5 y (22% died), and in group 1 was 7.3 y (only 8% died): group 3 > group 2 > group 1 (P < 0.01). Late radiotherapy toxicity was higher in group 3 (n = 17; 65%) and group 2 (n = 17; 59%) than in group 1 (n = 3; 9%): group 3 ≃ group 2 > group 1 (P < 0.001). QoL was worse in groups 3 and 2 than in group 1: group 3 ≃ group 2 < group 1 (P < 0.002). Worse radiotherapy toxicity, QoL, and mortality were associated with deteriorated nutritional status and intake (P < 0.001). Likewise, depleted intake, nutritional status, and QoL predicted shorter survival and late toxicity (HR: 8.25; 95% CI: 2.74, 1.47; P < 0.001). Conclusions: This study conveys novel information about the effectiveness of nutrition at improving long-term prognosis in colorectal cancer. Overall, the data indicate that early individualized nutritional counseling and education during radiotherapy is valuable for patients.