Abstract: We report a case of febrile ulceronecrotic Mucha-Habermann disease (FUMHD) in a 34-month-old boy. Our patient had a history of biopsy-proven pityriasis lichenoides et varioliformis acuta (PLEVA) since age 2. At 34 months, his skin lesions rapidly progressed to ulceration and necrosis in the setting of high fever. Skin biopsy revealed an intense lichenoid infiltrate with parakeratosis at the edges of areas of epidermal necrosis consistent with FUMHD, which is the severe variant of PLEVA. Despite initial treatment with prednisolone, his disease progressed to involve more than 50% of his body surface area. In addition to corticosteroids, he was treated with intravenous immunoglobulin, dapsone, and acyclovir, without complete resolution of disease. Methotrexate successfully cleared his skin disease and systemic symptoms. This patient highlights the exceptional response of FUMHD to methotrexate. Based on our review of the literature, this also represents the youngest reported case of FUMHD.