Tinea incognito is a ringworm infection modified by corticosteroids. We report a case of a 2-year-old girl who developed tinea incognito due to Trichophyton mentagrophytes after applying methylprednisolone aceponate for 3 months. Diagnosis was confirmed by histopathologic and mycological examination, which led to the identification of Trichophyton mentagrophytes var. mentagrophytes, a zoophilic dermatophyte. Previous corticosteroid use in dermatophyte infections can alter their clinical appearance leading to misdiagnosis and delay in appropriate therapy.