Aim: This study aims to assess the existence of inflammation in the physiopathology of lateral epicondylitis (LE) and to evaluate the levels of blood inflammation parameters. Material and Method: 72 patients with LE and 50 healthy individuals were included in this retrospective study. Age, gender, erythrocyte sedimentation rate (ESR), neutrophil, white blood cell (WBC), C-reactive protein (CRP), lymphocyte, platelet counts, platelet-lymphocyte ratio (PLR), neutrophil-lymphocyte ratio (NLR) and systemic immune-inflammation index (SII) levels were scanned retrospectively from the hospital information system. Results: While the patient and control groups were similar in terms of gender, age, CRP, ESR, lymphocyte, NLR and PLR values (p=0.902, p=0.108, p=0.193, p=0.902, p=0.523, p=0.140 and p=0.253, respectively), the median value of neutrophils, mean platelet, mean WBC and median SII score parameters were higher in the patient group (P=0.022, p=0.037, p=0.037, p=0.038, respectively). A strong correlation was detected between SII and NLR and PLR (both p<0.001, r:0.833 and r:0.778, respectively). The area under the curve (AUC) was calculated as 0.61 for SII via the receiver operating characteristics (ROC) curve analysis, (p=0,038). Conclusion: The SII value, which is an indicator of inflammation, was more elevated in the LE group than in the healthy group. More study is needed on this subject.