Five cases of intact adult male crossbred cats presenting myiasis caused by the New World Screwworm Cochliomyia hominivorax (Diptera; Calliphoridae) are to be presented. Among those, three were stray animals admitted in a Veterinary clinic, one presenting a left humerus fracture and the other two, extensive lesions in the anterior part of body. The other two were domiciliated cats previously submitted to cryosurgery readmitted in the Small Animal Hospital of the Universidade Federal Rural do Rio de Janeiro few weeks later. One was treated to epidermoid carcinoma and the other facial lesions due to sporotrichosis. Lesions cleansing, debridement of necrosed tissues and mechanical removal of accessible larvae were performed in all animals. For supplementary larval removal, nitenpyram (Capstar® Novartis) was orally administered. As support treatment flunixin meglumine and enrofloxacin were administered. Larvae were mechanically removed from all animals and fixed for posterior identification. Maggots were classified as third instar C. hominivorax larvae. Stray cats died despite the given treatment due to their lesions severity. In contrast, domiciliated animals were completely recovered. Nitenpyram lead to the expected expulsion and larvicidal effects when administered to infested cats as seen in parasitized dogs. The fact that all the animals were intact crossbred males corroborates with the literature. This is because of territorial and reproductive competitive fighting that intact males are prone, leading to trauma. Additionally, free roaming cats are more likely susceptible to accidents, such as canine attacks. In the present study, domiciliated cats were successfully treated once the diagnoses were made in an earlier phase, besides the limited extension and non fatal localization of wounds. The cause of myiasis installation in both cases was owner's neglect after surgical procedures. In contrast, the stray cats had massive infestation in extensive lesions. Diagnosis and treatment in stray cats are known to be difficult. Clinical case reports of the New World screwworm myiasis are relevant due to its importance and frequent occurrence in feline veterinary routine in many countries, especially in outdoor intact male cats. In this matter, veterinarian clinician of small animals should inform owners about prevention methods and how to recognize the infestation as soon as possible, avoiding significant damages to their cat's health.