In the article the case of diffuse lymphangioleiomyomatosis of the lung at 21 year-old women is described The disease has manifested on the 38th week of the pregnancy. Leiomyomas of others localizations were absent. The clinical course was malignant: in 22 days after disease's manifestation women had died. The possible mechanisms of uncontrolled proliferation of nonstriated muscle's elements and features of lymphangioleiomyoma's morphological diagnostics are discussed.