Ultrasonography is a useful tool in order to provide information regarding diaphragm function, especially in cases where local pathology coexists, as in pleural effusions or traumatic rupture. Ultrasound can also be used as a method for analyzing diaphragmatic movement using M-mode. M-mode sonography appears to be a simple, well tolerated, reproducible method of assessing hemidiaphragmatic movement. Its advantages are lack of risk from ionizing radiation, portability and direct quantitative information regarding the amplitude, duration and velocity of hemidiaphragmatic movement. By quantifying diaphragm function, one might be able to predict the timing for successful weaning from mechanical ventilation, evaluate diaphragm function during drug therapy, and assess mechanical ventilation strategies designed to strengthen the diaphragm.