The paper describes a case history of a 64-year-old woman who had suffered over no less than 2-year period from an unusual hormonally active tumour of the parathyroid gland associated with signs characteristic of Reklinghausen's disease. The tumour presented a node 4 cm in diameter. Histologically it showed pronounced atypia and polymorphism of the cells of the chief cell type and eosinophilic cells. Grimelius silvering revealed not numerous cells with argyrophil granularity in the cytoplasm. No mitoses were detected but tumour cells grew into the capsule of the node. No metastases were found on autopsy 20 days after the operation.