Background: Various studies describing the clinical characteristics of patients with COVID-19 pneumonia have shown that patients with a severe disease course have a tendency to have higher C-reactive protein (CRP) levels, neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR). Aims: The aim of this study was to determine whether or not there was a correlation between the CRP value, NLR, and PLR, which are simple, effective, and repeatable predictive values, and the lung involvement severity score determined from the thoracic computed tomography (CT) findings of patients with COVID-19 pneumonia. Methods: This retrospective study included 200 patients admitted to the COVID-19 clinic of Erzincan Binali Yildirim University Mengucek Gazi Training and Research Hospital between 01.10.2020 and 31.12.2020. The thoracic CT examination results and CT scores of the patients were recorded. The relationships were investigated between the thoracic CT score and the systemic inflammatory mediator levels. Results: A positive correlation was determined between the radiological scoring and NLR at a weak level (r=0.22, p=0.001), PLR at a weak level (r=0.18, p=0.012) and CRP at a moderate level (r=0.43, p<0.001).