Résumé : Abstract Background Cytoreductive surgery (CRS) for peritoneal metastases of colorectal cancer (PMCRC) is associated with a high risk of postoperative morbidity, thus making patient selection of upmost importance. Further to data showing an association between preoperative serological biomarkers and patient outcome in various solid tumors, in this study we aim to evaluate their prognostic value in patients with PMCRC treated with curative intent. Patients and Methods This is a retrospective study including patients with PMCRC treated by complete CRS ± HIPEC at our institution between 2011 and 2020. Preoperative serological biomarkers, along with other standard clinicopathological variables, were studied to determine their prognostic value. Results A total of 94 out of 108 patients met the inclusion criteria. Forty-three patients (46%) presented with synchronous PM. The median peritoneal cancer index (PCI) was 6. On univariate analysis, a higher neutrophil-to-lymphocyte ratio (NLR) was associated with poor prognosis in terms of overall survival (OS) [cutoff 3.567, hazard ratio (HR) 2.8 (1.4–5.3), p = 0.002], whereas a higher platelet-to-lymphocyte ratio (PLR) predicted favorable prognosis in terms of disease-free survival (DFS) [cutoff 185.4, HR 1.9 (1.07–3.53), p = 0.030]. On multivariate analysis, NLR > 3.567, positive lymph nodes (LNs), and PCI > 7 were independent predictive factors for worse OS, whereas NLR > 3.567 and positive LNs were significantly associated with worse DFS. PLR > 185.4 was associated with better DFS. Conclusion High preoperative NLR (> 3.567) and PLR (> 185.4) can predict outcome of patients with PMCRC treated by complete CRS ± HIPEC.