Background: Coronavirus disease-2019 (COVID-19) can cause asymptomatic, mild upper respiratory tract symptoms, pneumonia in young persons. How the disease will progress in each patient is still unknown. Therefore, we aimed to investigate the prognostic markers of the development of pneumonia and the clinical characteristics of patients under 65 years with COVID-19 confirmed by a positive reverse transcriptase polymerase chain reaction (RT-PCR) test. Method: In this retrospective study, a total of 271 patients admitted in our unit were included. The patients were divided into two groups, those who did or did not develop pneumonia. Their clinical features, treatment protocols and laboratory parameters were recorded retrospectively. Results: Pneumonia developed in 67.9% (n = 184) of the cases. Age in the pneumonia group was higher than in the non-pneumonia group (p < 0.001). In the logistic regression analysis, when symptom and comorbidity status were examined according to the presence of pneumonia; HT (OR: 4,525 95% CL: 1,494–13,708) were the most important risk factor for pneumonia. When age and laboratory values were examined according to the presence of pneumonia, advanced age (OR: 1.042 95% CL: 1.01–1.073), low albumin (OR: 0.917 95% CL: 0.854–0.986) and high troponin (OR: 1.291 95% CL: 1.044–1.596) were identified as risk factors for pneumonia. Conclusion: HT, older age, low albumin, high troponin were important factors for predicting COVID-19 pneumonia in patients under 65 years of age. Young patients with these predictive factors should be more carefully evaluated by further diagnostic procedures, such as thoracic CT. Key Words: COVID-19, pneumonia, young adults