Background: There are many methods of evaluating diaphragmatic function, includingtrans-diaphragmatic pressure measurements, which are considered the key rule of diagnosis. We studied the clinical usefulness of chest ultrasonography in evaluating stablechronic obstructive pulmonary disease (COPD) patients and those in exacerbation,focusing on diaphragmatic measurements and their correlation with spirometry andother clinical parameters. Methods: In a prospective case-control study, we enrolled 100 COPD patients dividedinto 40 stable COPD patients and 60 patients with exacerbation. The analysis included20 age-matched controls. In addition to the clinical assessment of the study population,radiological evaluation included chest radiographs and chest computed tomography. Transthoracic ultrasonography (TUS) was performed for all included subjects. Results: Multiple A lines (more than 3) were more frequent in COPD exacerbation thanin stable patients, as was the case for B-lines. TUS significantly showed high specificity,negative predictive value, positive predictive value, and accuracy in detecting pleuraleffusion, consolidation, pneumothorax, and lung mass. Diaphragmatic measurementswere significantly lower among stable COPD subjects than healthy controls. Diaphragmaticthickness and excursion displayed a significant negative correlation with bodymass index and the dyspnea scale, and a positive correlation with spirometry measures. Patients in Global Initiative for Chronic Obstructive Lung Disease (GOLD) groupD showed lower diaphragmatic measurements (thickness and excursion). Conclusion: The TUS of COPD patients both in stable and exacerbated conditions andthe assessment of diaphragm excursion and thickness by TUS in COPD patients andtheir correlations to disease-related factors proved informative and paved the way forthe better management of COPD patients.