Deep stromal vascularization was observed in corneas of four cynomolgus monkeys after extended monocular hydrogel contact lens wear. Keratocytes and extravascular leukocytes, including macrophages, lymphocytes, and in one case, neutrophils, were associated with the vessels in three monkeys. Vessel regression was observed in some animals, but not when lens wear was continuous. In one animal, neutrophil infiltration of the stroma associated with gross epithelial edema was observed. Involution of neutrophils by apoptosis and phagocytosis of pyknotic cells by macrophages was noted. The present study describes the ultrastructural features of deep corneal vascularization developed during extended contact lens wear and illustrates an association between leukocytes and new vessels.