[Primary pulmonary histiocytosis X]

The diagnosis of a pulmonary form of histiocytosis X was made on the basis of a lung tissue biopsy in a male aged 60 suffering from progressive dyspnoe of respiratory type and a rentgenological finding of tiny disseminated foci in both lung fields. The bad prognosis of the process related to the fibrous transformation of neoplastic foci rather than to the biological nature of the process as such.