Aim: Total knee arthroplasty (TKA) is an effective and successful procedure but the outcome may occasionally be compromised by complications such as periprosthetic joint infection (PJI). Blood neutrophil to lymphocyte ratio (NLR) is a simple marker of subclinical inflammation that can be easily obtained from the differential White Blood Cell count. This study aims to to analyze the predictive ability of NLR for the diagnosis of PJI. Material and Method: Patients who were diagnosed as grade 4 gonartrosis and operated for total knee arthroplasty between years 2007-2014 were evaluated. Thirty patients with PJI were included in the study as Group I and hematological tests including erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), white blood cell count (WBC) and neutrophil to lymphocyte ratio (NLR) of the patients were evaluated retrospectively. Preoperative and postoperative 6th month NLR values of the patients were compared. Also 103 age matched patients operated for total knee arthroplasty with no sign of infection were included in the study as controls (Group II). Patients in Group I and Group II were also compared in terms of NLR. Results: Thirty patients (17 female, 13 male) were present in Group I (patients with PJI and treated with two staged revision surgery) and 103 patients (94 female, 9 male) were present in Group II (patients operated for total knee arthroplasty and had no sign of infection during the follow up period). NLR has been found to decrease from 3.2+/-0.7 to 2.2+/-0.5 when compared between the preoperative and postoperative 6th month period (p=< 0,001). NLR has been found to be 2.1+/-0.7 in Group II and 3.2+/-0.7 in Group I at preoperative period. (p=< 0,001). The value of 2.45 was found to be cut-off point for infection. Discussion: NLR can be used as marker for PJI together with the other markers as ESR and CRP to increase the accuracy of the diagnosis.