Lymphangioleiomyomatosis and Langerhans cell Histiocytosis are two different diseases that can involve the lungs, with unknown etiology and origin. Both are rare, present a similar radiological pattern (multiple nodules and cysts in the lungs) and may have a similar clinical presentation, with progressive dyspnea, hemoptysis, pneumothorax and a variable course usually culminating in respiratory failure. Due to these similarities a differential diagnosis may be difficult in some instances. This review underlines differences in epidemiology, pathogenesis and prognosis that could assist clinicians in making a differential diagnosis of these rare and severe pulmonary diseases.