<p>This study assessed the significance of both the pre- and postoperative neutrophil-to-lymphocyte ratio (NLR) in patients with stage II and III colorectal cancer who underwent colorectal surgery and evaluated the clinical outcomes. This retrospective study included 223 patients who underwent colorectal surgery for stage II and III colorectal cancer from January 2013 to July 2019. Patients were divided into four groups according to the pre- and postoperative NLR (high or low): Group 1 (G1, low and low; <i>n</i> = 122), Group 2 (G2, high and low; <i>n</i> = 29), Group 3 (G3, low and high; <i>n</i> = 34), and Group 4 (G4, high and high; <i>n</i> = 38). The impact of the pre- and postoperative NLR on the time to the recurrence-free survival (RFS) and overall survival (OS) was evaluated. The Kaplan–Meier survival curves for the RFS and OS in stage II and III colorectal cancer indicated a decline in G3 and G4, with a more pronounced decline being noted in G4 (<i>P</i> &lt; 0.001 and <i>P</i> &lt; 0.001, respectively). Subgroup analyses of stage II disease showed that both the RFS and OS were poor, particularly in G3 and G4. Regarding stage III disease, there was a tendency for a worse prognosis in RFS for G3 and G4, and in OS for G2 and G4. This study suggests that postoperative NLR is a prognostic marker for RFS and OS in patients with stage II and III colorectal cancer. These results indicate that, particularly when both the preoperative and postoperative NLR are high, these findings may be a high-risk factor for the recurrence of colorectal cancer. This marker may serve as an indicator to help determine the need for intensive postoperative surveillance and adjuvant chemotherapy.</p>