Background : Ultrasound has become an invaluable resource in the assessment of chest abnormalities, in which liquid and solid densities are interposed between the chest wall and the lungs, allowing excellent propagation of sound waves, making it possible to extend the use of ultrasound in the diagnosis of a number of chest diseases. Aim of the work : Assessment of the role of transthoracic ultrasound in the diagnosis of some chest diseases. Subjects and methods : The present study was conducted in Chest Department in collaboration with Tropical Department, Kasr El-Aini hospital in the period from June 2010 to January 2011. It included 31 patients who fulfilled the selection criteria & formed the study population. The patients were subjected basically to full history taking, full clinical examination, chest x-ray. All patients were examined by transthoracic ultrasonography, ultrasound guided biopsies and ultrasound guided aspiration of pleural fluid was done whenever indicated. CT chest and CT guided biopsies were also done whenever indicated. In cases of pleural effusion the pleural fluid was sent for chemical, bacteriological and cytological examination to study the relationship between the ultrasonographic findings of pleural effusion and the nature of pleural fluid. Also findings of transthoracic ultrasound were compared to findings of CT chest. Results : The total number of diagnosed cases was 28 patients out of 31 patients who represent the study population. The most frequent method of diagnosis was the US guided biopsies (16 cases) followed by US guided aspiration of pleural fluid (6 cases). 1 case was diagnosed by C.T guided biopsy because the result of US guided biopsy was non-specific. 1 case was diagnosed by open biopsy because trials of US guided biopsy and C.T guided biopsy were failed. 3 cases were diagnosed by thoracoscopic biopsies. 1 case was diagnosed by bronchoscopic biopsy. Conclusion : The results of the study revealed that transthoracic ultrasonography and ultrasound guided biopsies are useful in diagnosis of variant chest diseases . Ultrasonographic findings of pleural effusion can help in detecting the nature of pleural fluid. No significant difference between the findings detected by transthoracic ultrasonography and CT chest.