We report the case of a 5-year-old girl who developed a remarkably extensive kerion of the scalp due to Microsporum canis infection. Total scalp involvement of this severity and prolonged duration is now unusual, but there has been surprisingly little residual cicatricial alopecia. Microsporum canis does not respond well to ketoconazole, and griseofulvin remains the drug of choice for dermatophyte infections involving hair; a prolonged course may be necessary. This case also demonstrates the benefit of corticosteroids for certain cases of inflammatory ringworm where the host's response to the fungus is exceptionally marked.