Mycetoma is a chronic subcutaneous tumefaction with presence of grains or granules. Etiological agents include bacteria or filamentous fungi. Mycetoma due to dermatophytes is uncommon, mainly occurring in Africa. To our knowledge, no case has been reported in the West Indies. Only two observations of Micosporum canis mycetoma in humans have been reported in the literature. We report a third case of mycetoma of the scalp caused by this fungus.A 22-year-old woman from Martinique, French West Indies, presented with an indolent tumefaction of the scalp evolving over five years. She had mental retardation due to congenital adrenal hyperplasia with 21-hydroxylase deficiency. The lesion was extracted surgically. Pathology and mycology examinations showed features of Microsporum canis mycetoma. Two months later, the scalp lesion recurred and the patient was treated with griseofulvin after surgical extraction.Mycetoma due to dermatophytes is very uncommon, mainly observed on the scalp and nape of the neck. A history of a skin lesion is frequent, leading to transcutaneous penetration of the fungus and mycetoma formation. Several dermatophyte species have been identified as causal agents (Microsporum ferrugineum, Trichophyton rubrum, Trichophyton verrucosum, Trichophyton mentagrophytes, Microsporum audouinii, Microsporum langeronii). Microsporum canis is rarely demonstrated in humans: two cases in children in Africa and Australia. Our observation was similar to the two cases in the literature: indolent and mobile tumefaction of the scalp, in a child or young adult, suggestive of lipoma or epidermal cyst, with excision leading to diagnosis. Association with tinea capitis and skin or nail involvement can also be observed.