An electron microscopic study of a cutaneous lesion of lymphomatoid granulomatosis taken from a patient with pulmonary involvement was performed. Microvascular alterations ranged from mild, degenerative changes to vessel necrosis. Less severe changes included enlarged endothelial cells, with margination of small lymphoid cells in affected vessels. Luminal occlusion by necrotic endothelial cell fragments and fibrin was associated with thickening and reduplication of the basal lamina and an angiocentric, inflammatory infiltrate in severely affected vessels. The most frequently observed cells in the infiltrate were cleaved and noncleaved lymphocytes that exhibited notable cytolysis and degenerative changes in cytoplasmic organelles. We conclude that lymphomatoid granulomatosis involving the skin is a disorder in which substantial numbers of cleaved and noncleaved lymphoid cells participate, eventuating in small-vessel necrosis and occlusion and repeated endothelial cell regeneration.