Aim: Coronavirus-2019 (Covid-19) primarily affects the respiratory system, and how it affects respiratory muscles and lung volume is still not fully understood. Our study aimed to assess the time-dependent changes that may occur in lungs and respiratory muscle sizes on chest computed tomography (CT) in adult coronavirus disease 2019 (COVID-19) patients.Material and Methods: The clinical and radiological records of 101 adult patients who had at least two non-contrast chest CT images in stage 1 (0-4 days) and stage 6 (>28 days) were collected retrospectively. ImFusion Suite program were used to calculate lung volumes, and the cross-sectional areas of the pectoral and intercostal muscles were also calculated using with “ImageJ” program.Results: One-hundred one patients (51 females, 50.49%) were included in the study. ANCOVA revealed a significant stage*side interaction effect regarding cross-sectional area (CSA) of intercostal muscles [(p=.010; η²p=.064)]. There was no significant difference between the two stages in terms of CSA of pectoralis major and minor muscles [(p=.314; η2p=.010), (p=.644; η²p=.002)] respectively and lung volume [(p=.340; η²p=.009)].Conclusion: Covid-19 pneumonia causes an atrophy in respiratory muscles. However, it seems to have a nonsignificant effect on auxiliary respiratory muscles and lung volume. Further investigation of respiratory muscles and respiratory muscle training to reduce the risk of serious complications during viral infections are required.