Objective: Demographic and laboratory values predicting clinical severity in coronavirus disease 2019 (COVID-19) patients havebeen a matter of curiosity since the beginning of the disease. We aimed to show the relationship between the severity of COVID-19disease and comorbidities, clinical and laboratory features of the patients.Material and Method: The data of COVID-19 patients diagnosed with polymerase chain reaction (PCR), were analyzed retrospectively.The patients were divided into 3 groups according to their clinical severity as mild, moderate and severe. Comorbidities and theCharlson comorbidity index (CCI) at the time of diagnosis were calculated for each patient from the patients’ records. Demographicdata, laboratory values, comorbidity and CCI scores were compared between the patient groups. The effect of CCI on survival andlength of hospital stay was examined.Results: One hundred and four patients were included in the trial. The most common comorbid disease in the patients included in thetrial was hypertension. The moderate-severe stage patients were statistically significantly older (p<0.001). The CCI was found to bestatistically significantly different between mild, moderate and severe groups (p<0.001). When CCI increases by one unit, the risk ofdeath increases by 1.193 times (p=0.017). The neutrophil-to-lymphocyte ratio (NLR) was statistically significantly different betweenthe mild, moderate and severe patient groups. It was observed that as the severity of the disease increased, the NLR increased. Olderage, WBC, neutrophil count, NLR, BUN, creatinine, AST, potassium level, C-reactive protein (CRP), procalcitonin, aPTT, fibrinogen,d-dimer, and ferritin levels were found to be higher in the clinically severe patient group. Lymphocyte and eosinophil counts, totalprotein, albumin and sodium levels were found to be lower in the clinically severe patient group.Conclusion: This trial showed that calculating the CCI score in COVID-19 patients can be useful in predicting the severity of thedisease. Examination of CCI, age, WBC, neutrophil, lymphocyte, eosinophil counts, BUN, creatinine, AST, total protein, albumin,sodium, potassium level, CRP, procalcitonin, aPTT, fibrinogen, d-dimer and ferritin levels at the time of diagnosis can be suggested.