AbstractWe report the case of a 73 year old woman who presented for progressive dyspnea. Her medical history included thyroidectomy 15 years ago, myocardial infarction, recurrent paroxysmal atrial fibrillation and femoral fracture two weeks previously, conservatively treated. Physical examination revealed absent breath sounds in the left hemithorax, up to the apex, and crackles in the right hemithorax. The acid-base balance showed acute hypoxemic respiratory failure. The chest X-Ray revealed left diaphragmatic paralysis. Thoracic CT-scan was performed, which excluded the pulmonary embolism and revealed left diaphragmatic relaxation, ascension of the splenic angle of the colon, stomach and spleen up to the projection of left lung hilum, and right postero-basal alveolar condensation process. Diaphragm dysfunction can be caused by various disorders, including phrenic paralysis. This pathology should be considered in the differential diagnosis of acute respiratory failure.