Crystal-storing histiocytosis (CSH) is a rare process most often occurring in conjunction with an underlying hematopoietic neoplasm, usually multiple myeloma or low-grade B-cell lymphoma. We report the first case of pulmonary CSH diagnosed by fine-needle aspiration biopsy. A patient with a history of urothelial carcinoma developed a lung nodule, which was evaluated by fine-needle aspiration biopsy. Cytologic examination revealed macrophages with abundant cytoplasmic crystals diagnostic of CSH. Based on this cytologic interpretation, additional clinical laboratory evaluation was pursued and revealed a previously unknown monoclonal serum protein. CSH must be differentiated from other non-neoplastic and neoplastic lesions and when diagnosed, should trigger a search for an underlying lymphoproliferative disorder.