Two cases of hypoglycemiant pleural fibroma are reported: -- the first case, in a patient with sarcoidosis, was diagnosed following the onset of neuropsychic manifestations due to hypoglycemia; --the second case, much more atypical, was a patient with an enormous pleural tumor affecting cardiorespiratory function to such a degree that almost total incapacity ensued: the hypoglycemia was detected during routine pre-operative investigations. Various extrathoracic manifestations accompany these tumors: osteo-articular (present in 1 patient), and thyroidal (present in both cases). The various mechanisms proposed to explain the development of hypoglycemia in patients with certain extra-pancreatic tumors are reviewed.