The presence of nosocomial myiasis reflects a lack of adequate medical attention, due to the physical facilities and/or the health care personnel. Patients requiring special attention are more susceptible, such as those with a loss of consciousness, assisted mechanical ventilation, tracheal tubes, or nasogastric probes. Nosocomial myiasis is a rare event that has a greater occurrence in the hospitals of poor and developing countries. The two cases herein described represent the first report of nosocomial myiasis in Mexico. The causal agents were found to be Lucilia sericata and Sarcophaga spp. The taxonomical identification of the larvae of the second and third instar was based on the morphology of the cephaloskeleton, anterior spiracles, and peritreme plaques.