A 62-year-old man who had smoked 15 cigarettes per day for 42 years was referred to our hospital because of non-productive cough and an abnormal chest shadow. Chest computed tomography (CT) scan revealed multiple micronodules and small centrilobular nodular shadows in both lung fields. We performed bronchoalveolar lavage (BAL) into the right B⁵b and fiberoptic transbronchial lung biopsy (TBLB) of the right B⁴, B⁸, and B⁹. Although the TBLB specimens showed non-specific inflammation, histopathological findings of the cell block obtained by BAL revealed 8.0% of the BAL cells to be positive for CD1a immunocytochemically. From these observations, we finally diagnosed him with pulmonary Langerhans cell histiocytosis (PLCH), and most of the shadow on chest CT scan had disappeared 4 weeks after cessation of smoking. We report a case of PLCH successfully diagnosed using cell block from the BAL.