Chest radiography is standard for the diagnosis of a pneumothorax. However, also ultrasound of the chest has considerable value in the detection of a pneumothorax. A typical sonographic feature is the lack of the lung gliding sign. Aim of our trial was to evaluate the significance of ultrasound of the chest in the diagnosis of a pneumothorax supplemented by using power colour Doppler imaging.Following transbronchial biopsy, patients received transthoracic ultrasound of the chest for evaluation of a pneumothorax. Immediately afterwards, a chest radiograph was performed and results were compared.1023 patients (321 female, 702 male, median age 47 years) were examined. In 30 patients (2.9%) chest radiograph revealed a pneumothorax, while in ultrasound of the chest a pneumothorax was diagnosed in 36 of the cases. Defining chest radiography as gold standard, ultrasound of the chest had a sensitivity of 100%, a specificity of 83% and an accuracy of 99%.Transthoracic ultrasound of the chest is a highly sensitive and specific diagnostic tool in the diagnosis of a pneumothorax. In comparison to chest radiography, it is better available and prevents administration of ionizing radiation. However, a disadvantage of ultrasound is the lack of quantification of a pneumothorax and the assessment of the indication for chest tube drainage.