Alternaria is a very common and saprophytic fungus. Cutaneous infection is rare and about 71 cases have been described, mainly in Europe in immunocompromised hosts. We report a case of dermal alternariosis occurring in a woman treated with corticosteroids for dermatomyositis. The cutaneous lesion consisted of an erythematous and scaly plaque on the leg measuring 2 x 2 cm. Cutaneous biopsy showed hyphae and round inclusions stained with PAS and Gomori-Grocott within a polymorphous granuloma. Cultures of cutaneous biopsies grew Alternaria sp. HIV1 and HIV2 serology was negative. The patient was treated by local excision and corticosteroids were decreased. One-year follow-up showed no recurrence. Cutaneous alternariosis is an opportunistic infection. the disease has been described mainly in patients treated with systemic corticosteroids (39 cases out of the 71 reported cases) or local corticosteroids (3/71) and in patients suffering from Cushing's syndrome (7/71) but rarely in HIV-infected patients (3/71). Cutaneous fragility induced by hypercorticism is an important cofactor permitting direct inoculation from the environment.