Pulmonary Langerhans’ cell granulomatosis (LCG) is a diffuse, smoking-related lung disease characterised pathologically by bronchiolocentric inflammation, cyst formation, and widespread vascular abnormalities, and physiologically by exercise limitation. Pulmonary fibrosis is a long term sequel. Diagnosis may be made by lung biopsy and by bronchoalveolar lavage (BAL). The papers by Gabbay et al 1 and Habib et al 2 present two cases of LCG which recurred after double lung transplantation at two years and four years, respectively. These are the first reports of recurrent LCG in the transplanted lung. As lung transplantation is now recognised as a treatment for this disease, these two reports serve to draw our attention to what may prove to be the beginning of a series of such cases. The titles of these two papers1 2 also draw our attention to the remaining confusion about the terminology of this disease. This confusion has been based upon historical morphological reports. The “histiocytoses” are reactive or proliferative diseases of cells of the mononuclear phagocyte system classically seen in childhood, and they include Langerhans’ cell histiocytosis (LCH) or granulomatosis (LCG), haemophagocytic syndrome (familial and reactive), sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease), juvenile xanthogranuloma, and malignant …