Introduction: The most prevalent method for evaluating lung expansion in high-frequency oscillatory ventilation (HFOV) is chest X-ray (CXR). The purpose of this study was to compare the accuracy of chest radiography with point-of-care ultrasound (POCUS) in determining lung expansion. Methods: This prospective study included newborns who required HFOV and were being monitored in the Neonatal Intensive Care Unit. A single neonatologist assessed lung expansion with a chest x-ray and POCUS, to measure the costal level of the right hemidiaphragm and compare the results. Results: A neonatologist took 55 measurements on 28 newborns with a gestational age of 32 (23.2-39.4) weeks who were followed on HFOV. The rib counts obtained from anterior chest ultrasonography and posterior CXR showed a statistically high concordance (p<0.05). Conclusions: Lung ultrasonography is a reliable method in the evaluation of lung expansion in patients followed on HFOV.