Objectives: Cochlear implant (CI) infection is the most common complication after CI surgery. We investigated whether the preoperative neutrophil–lymphocyte ratio (NLR) and platelet–lymphocyte ratio (PLR) values could predict the CI infection and the NLR and PLR values obtained at the first admission to the hospital with an CI infection could help the clinician in the diagnosis. Methods: This retrospective case-controlled study included 26 patients with postsurgical CI infection. To prevent age-related incompatibility in the blood analysis of the infected group, the patients were divided into three age groups: 0–4 years, 5–18 years, and over 18 years old. To compare the infected group, 29 patients who did not have implant infection after CI surgery and whose age ranges were compatible with the infected group were randomly selected from the hospital records as the control group. The infected group preimplantation (PREs) and postinfection (POSTi) NLR and PLR values were compared with each other and the control group values. The area under the curve, sensitivity, specificity, and cutoff values were calculated by ROC analysis. Results: The POSTi NLR values of the infected group patients aged 0–4 years and over 18 years were significantly greater than the PREs NLR values (p =.038 and p =.008, respectively). Significant differences were found between the POSTi NLR values of the infected group patients aged 0–4 years and over 18 years and those of PREs in the control group (p =.011 and p =.015, respectively). Conclusions: Preoperative NLR and PLR values cannot predict postoperative CI infection. However, NLR and PLR values increased significantly after CI infection, even if systemic symptoms did not occur. At the first admission to the hospital, NLR values can guide the clinician in diagnosing the CI infection in patients between 0 and 4 years and over 18 years. Trial Registration Clinical Trials.gov Identifier: NCT04120181.