We report a new case of diffuse pulmonary lymphangiomatosis in a 22 year-old man with a dysmorphic syndrome. The disease started with dyspnea which became rapidly disabling. The diagnosis was established from a pulmonary biopsy. Our patient developed severe chronic respiratory failure. Diffuse pulmonary lymphangiomatosis is a very uncommon disease. It is seen predominantly in children, exceptionally in adults, and affects both sexes equally. Symptoms like dyspnea and cough, pulmonary function with restrictive pattern, and interstitial syndrome, are not specific. Only pathology is evocative, characterized primarily by multifocal proliferation of pulmonary lymphatic vessels and increased number of complex anastomosing channels. These channels tend to dilate with time. The prognosis is poor and the treatment essentially palliative.