Background: In order to determine the diagnostic perfor-mance of lung ultrasound in comparison with HRCT, thirty five patients with known history of positive features of interstitial lung diseases related to connective tissue diseases were recruit-ed in a prospective study. The patients' ages ranged from 18 to 74 years with a mean age of 43.3 years. They were evaluated by LUS and standard high resolution CT chest study (HRCT). Aim of Study: This study was to investigate the diagnos-tic accuracy of the LUS in the evaluation of interstitial lung disease changes due to systemic connective tissue disease in comparison to HRCT. Subjects and Methods: In the duration from August 2022 to January 2023, 35 patients with known history of connective tissue diseases and showing positive diagnostic features of in-terstitial lung diseases participated in this prospective study. All patients had thoracic ultrasound followed by high resolution CT chest examination following taking their consents. After-wards, final cases interpretation and data collection were done. Results: Following comparison and correlation with HRCT, LUS had sensitivity of 94.3%, specificity of 0% (as there were no negative results), PPV of 94.3% with an overall accuracy of 94.3% for the diagnosis of ILDs. There was a significant posi-tive correlation between the frequency of abnormalities detect-ed by HRCT and LUS. Conclusions: LUS is a low-cost, non-invasive, radia-tion-free and portable tool that can be rapidly performed. How-ever, it only assesses 70% of the lung surface, and only chang-es close to the pleural surface can be seen as well as it lacks specificity to ILD. In addition, LUS cannot identify the central or peri-hilar regions when compared to HRCT, so it could rep-resent a complementary screening, evaluating and follow-up approach of CTD-ILD.