Background: Although chest X-ray is the main imaging approach in many settings, many limitations for it exist. Ultrasound has quite similar performances to CT with many advantages. Methods: From January 2017 till May 2018, a prospective cohort study conducted in emergency ICU at Zagazig university hospitals including 124 critically ill patients older than 18 years with respiratory distress, cough, fever, or hypoxemia. We excluded from the study pregnant females, patients with massive chest wall emphysema or hematoma, morbidly obese and finally patients with risk of transportation. All patients underwent thorough physical examination, history, laboratory investigations & Chest radiology (X-rays, chest ultrasound & CT). We measured the sensitivity and specificity of chest ultrasound and chest X-rays in comparison with CT with measurement of the learning curve of chest US. Results: 124 patients were assessed for eligibility. 24 patients were excluded for different causes and 100 patients (69 males & 31 females) completed the study with mean age of 49.22±11.52 years. Regarding all study population, whatever diagnosis, sensitivity and specificity of chest ultrasound and chest X-rays were 91.4%, 98.3% and 61.7%, 96.2% respectively. Concordance of the results of ultrasound with results of X-rays and clinical diagnosis increased sensitivity, specificity and overall accuracy to highly comparable results with chest computed tomography. Sensitivity, specificity and accuracy of chest ultrasound increased with time and with number of patients. Conclusions: Chest ultrasound is reliable, quick, bedside, low-cost, non-invasive, non-ionizing, more accurate, and easily educated for early detection of chest diseases and their follow up.