Evaluation of histopathological and ultrastructural changes in skin eruptions of three dengue fever patients was performed. The main pathological findings in skin lesions were swelling of the endothelial cells in small vessels of papillary dermis, diapedesis of neutrophils, extravasation of erythrocytes and perivascular mononuclear cells infiltration. Ultrastructural observation revealed degeneration of endothelial cells and neutrophils. The relationships among endothelial cell damage, cell infiltration and hemorrhage were discussed.