We evaluated CD1a-positive cells in bronchoalveolar lavage samples from children with Langerhans cell histiocytosis (LCH). All children with multifocal LCH and pulmonary symptoms scored higher than 5% (30.6% +/- 7.2%), whereas those with other lung disorders scored much less than 5%. In children with multifocal LCH, bronchoalveolar lavage fluid abnormalities can precede pulmonary symptoms. During chemotherapy the CD1a-positive cell count lends to decrease.