ABSTRACT Background: This study was conducted to investigate the relationship between clinical course and pulmonary artery (PA) diameters in children diagnosed with COVID-19. Method: The study included 62 patients who presented COVID-19 symptoms between March 2020 and April 2021. Group 1 consisted of 32 pediatric patients who were COVID-19 PCR (+), while Group 2 consisted of 30 pediatric patients who were COVID-19 PCR(-). The data were collected retrospectively from medical records. Patients who developed pneumonia due to causes other than COVID-19 and those who had a history of pulmonary hypertension or pulmonary thromboembolism were excluded. The patients were examined based on their Computerized Tomographic (CT) findings, simultaneous whole blood parameters and biochemical parameters. Results: The thoracic CT findings of 18 of the patients in Group 1 were found normal. The CT images of 14 patients showed pulmonary involvement. Among the patients with pulmonary involvement, 8 had moderate pneumonia characterized by a ground-glass pattern, and 6 had severe pneumonia indicated by consolidation and linear opacities. The right pulmonary artery, left pulmonary artery and inferior vena cava (IVC) diameters of the patients in Group 1 were significantly higher than those of the patients in Group 2. Conclusion: The results of this study suggested that increased PA diameters in children diagnosed with COVID-19 may be accompanied by increased inflammation, high vascular resistance, hypoxemia and thromboembolic events. While it is thought that increased PA and IVC diameters are a factor that may indicate clinical deterioration in COVID-19 patients, more comprehensive studies are needed.