Human infection with botfly larvae (Cuterebra species) are reported, and 54 cases are reviewed. Biologic, epidemiologic, clinical, histopathologic, and diagnostic features of North American cuterebrid myiasis are described. A cuterebrid maggot generally causes a single furuncular nodule. Most cases occur in children in the northeastern United States or the Pacific Northwest; however, exceptions are common. Most lesions of North American cuterebrid myiasis are caused by second or third instar Cuterebra maggots that appear in late August, September, and October. First instar maggots are unusual and occur in the vitreous humor or in the upper respiratory tract of patients in late spring and early summer.