The occurence of chylothorax is uncommon and usually is caused by trauma or neoplastic process of the mediastinum. Primary lymphatic lesions of the lungs are extremly rare. One of them is lymphangiomatosis --diffuse lesions characterized primarily by an increased number of complex anastomosing lymphatic channels in which dilatation is secondary phenomenon. These lesions can involve lungs, mediastinum and pleura. The prognosis for the patients with this disease limited to the thorax is guarded and progressive although some patients have realtively indolent course. We present 2 patients : 18-years old boy and 17-years old girl. admitted to hospital because of chylothorax. The diagnostic did could not allow to discover disruption of thoracic duct, even during thoracoscopy. In material taken from the pleura and mediastinum during exploratory thoracotomy - diffuse pulmonary lymphangiomatosis was found. CT examination of the chest revealed osteolysis of the spine. The girl died after 6 weeks from the first symptoms and boy is observed for 18 months with symptoms of progressive restrictive lung disease.