This study investigated the usefulness of a novel inflammation-based prognostic system, named the COP-NLR (COmbination of Platelet count and Neutrophil to Lymphocyte Ratio), for predicting the postoperative survival of patients with colorectal cancer (CRC). The COP-NLR was calculated on the basis of data obtained on the day of admission: patients with both an elevated platelet count (>30 × 10(4) mm(-3)) and an elevated NLR (>3) were allocated a score of 2, and patients showing one or neither were allocated a score of 1 or 0, respectively. Four-hundred and eighty patients were enrolled. Multivariate analysis of clinical characteristics selected by univariate analysis showed that the COP-NLR (1, 2/0) (odds ratio, 0.464; 95% confidence interval, 0.267-0.807; P=0.007) had an association with cancer-specific survival, along with pathology, lymph node metastasis, the serum levels of carcinoembryonic antigen, C-reactive protein and albumin, and the Glasgow Prognostic Score. Kaplan-Meier analysis and log-rank test revealed that the COP-NLR was able to divide such patients into three independent groups (P<0.001). The COP-NLR is considered to be a useful predictor of postoperative survival in patients with CRC.