SummarySkin biopsies from the hands of twenty patients with myeloproliferative diseases (chronic myeloid leukemia, polycythemia vera, erythroleukemia and myelofibrosis) were studied by histological and histochemical techniques and electron microscopy, for the presence of microvascular lesions in the skin. In all cases there was a microangiopathy of variable intensity in the dermis. It was characterized by PAS positive thickening of the basal membrane and marked endothelial alterations with decrease of the vascular lumen. Electron microscopy showed a characteristic segmentary thickening of the basal membrane with an increased electron density and deposits of an amorphous material.The morphological and histochemical resemblance to the characteristics of the microangiopathy seen in diabetes is quite remarkable. There was no abnormality of the carbohydrate metabolism, and there must be quite different aetiological factors such as metabolic, immunological and haemodynamic.It would be interesting to investigate the aetiological aspects of this microangiopathy to understand how the biology of the malignant diseases produces the compromise of the microclrculation.