Ultrasound of 28 radiologically confirmed cases of pneumothorax were compared to 100 controls. Specific ultrasonographic signs were shown in all cases and could be categorised into four groups: isolated pneumothorax (n = 16), hydro-pneumothorax (n = 9), subcutaneous emphysema (n = 1) and post aspiration pneumothorax (n = 2). The isolated pneumothorax was characterised by the disappearance of the lung deflection signal. The effusion of the hydropneumothorax allows in addition a curtain sign which depicts the movement of the air/fluid level, the detachment of the lung being calculated across the liquid window whose echo-structure is analysed. Pneumothoraces appearing during an echo guided thoracic puncture are confirmed by the disappearance of the pathological image. Thus echography appears to be a new method in the diagnosis of pneumothoraces and is complimentary to standard radiology. It should be confirmed as particularly useful during the process of thoracic puncture or juxta-diaphragmatic puncture when following the process of a pneumothorax, for emergency situations and/or those in which no radiological equipment is available.