A 42-year-old woman who had a cigarette index of 420 had many cavitary lesions predominantly in the upper areas of both lungs. The lesions were detected on a health examination using CT. Analysis with bronchofiberscopy showed increased CD1a positive cells in bronchoalveolar fluid (BALF). Histological examination by video-associated lung biopsy demonstrated that both S-100 and vimentin-positive cells were present in the peribronchial fibrotic lesions. From these data, this disease was diagnosed as pulmonary Langerhans cell histiocytosis (PLCH). Three months after the cessation of smoking, the cavity lesions disappeared. As the image findings improved, CD1a positive cells in BALF decreased (4.9%→1.8%) and the CD4/CD8 ratio in BALF increased (1.66→6.16). So far, there is no report describing the time course of both CD1a positive cells and CD4/CD8 ratio in BALF after cessation of smoking in PLCH. These findings attract our interest on the PLCH.