Eight types of telangiectases were studied by light and electron microscopy and by 3-dimensional reconstruction from photomicrographs. Five were macular: mat telangiectasia of scleroderma, generalized essential telangiectasia, nevus flammeus, and 2 macular types not previously described. Three were papular: cherry angioma, angiokeratoma (Fabry), and angiokeratoma (Fordyce). The macular telangiectases were produced by dilatation of postcapillary venules of the upper horizontal plexus. There was no evidence of neovascularization or vascular malformation. The walls of the dilated venules were thickened by the peripheral deposition of basement membrane-like material admixed with reticulin fibers. The ultrastructure and configuration of the papular telangiectases were different. The cherry angioma was produced by spherical and tubular dilatations of capillary loops in dermal papillae. Each abnormally dilated loop was connected to the neighboring loop or loops by tortuous vascular channels. The vessels in the upper horizontal plexus were not involved. Ultrastructurally, the cherry angiomas were composed of both venous capillaries and postcapillary venules whose walls were thickened in a manner identical to that observed in the macular telangiectases. The angiokeratomas of Fabry and Fordyce were also produced by vascular abnormalities predominantly involving the dermal papillae. Ultrastructurally these vessels were similar to the small collecting veins which are normally found at the dermal-subcutaneous interface. Thus, the papular telangiectases also arose by alterations of the existing microvasculature rather than by proliferation of new vessels with random anastomoses. Reconstruction of the upper horizontal plexus from normal skin showed an undulating network of arterioles and their accompanying postcapillary venules. A 3-layered plexus arranged as venules, arterioles, and venules was not found.