In three years we encountered two patients with hospital-acquired myiasis, a rarely reported nosocomial problem. Both patients were elderly and had lengthy thoracic surgery in August in the same operating room. Larvae removed from the nares of one patient and from the chest incision of the other were of the same species, Phaenicia serricata. There was no evidence of tissue destruction or invasion in either case. Investigation revealed several factors that contributed to the presence of flies in the operating room. After a presumed environmental access site was closed and insecticide spraying was augmented, no additional cases occurred. This experience illustrates an unusual problem that may confront those responsible for infection control programs.