Dermatophytosis is one of the most frequent skin diseases of pets and livestock. Contagion among animal communities, high treatment cost, difficulties of control measures and public health consequences of animal ringworm are all factors urging the study of these fungi. Fungal disease agents are widespread and can be isolated from a wide range of sick animals or asymptomatic carriers, which can represent important reservoirs for people in close contact with them. This situation should be considered as an important risk factor for those with impaired immune systems and anyone working with or handling animals. The incidence of dermatophytosis caused by Microsporum canis is increasing in human patients in many places around the World, including several Brazilian cities, and it is often the predominant fungus seen in dermatological clinics.