ObjectiveCOVID-19 has been negatively impacted by a number of comorbidities. Aside from that, some conditions or treatments that cause immunosuppression can alter the course of the disease, leading to worse outcomes. The primary goal of this study is to compare the clinical presentation, laboratory analysis, radiological findings, and outcomes of patients with COVID-19 with and without immunosuppression.Materials and methodsThe study includes patients with pre-existing immunosuppression and COVID-19 infection who were admitted and received inpatient treatment at Marmara University Hospital, Istanbul, Pulmonary Medicine ward between April 2020 and June 2020. Data on demographics, epidemiology, clinical course, laboratory analysis, radiological findings, length of hospital stay, morbidity, and mortality were collected from all patients.ResultsThe study group consisted of 23 patients who had pre-existing immunosuppression, and the control group consisted of 207 immunocompetent patients, making a total of 230 patients. Significant differences in lymphocyte count, ROX (respiratory-rate oxygenation) index on Day 0, and fibrinogen levels were discovered between the two groups. SARI (severe acute respiratory infection) was more common in the control group than in the study group (p<0.022), but there was no difference in mortality.ConclusionThe mean number and percentage of lymphocytes were lower in immunocompromised COVID-19 patients at the time of diagnosis. Higher ROX index values and a lower risk of developing SARI could explain the hypothesis that these patients may be benefiting from a pre-existing corticosteroid regimen. Additional research with larger numbers of patients may be beneficial in drawing a more definitive conclusion.