Febrile ulceronecrotic Mucha–Habermann disease (FUMHD) represents a fulminant and potentially lethal variant of pityriasis lichenoides. Only 24 cases have been described so far. We report a 9-year-old boy who initially presented with classical pityriasis lichenoides et varioliformis acuta (PLEVA) following a mild enteritis. Three weeks later, his skin lesions started to ulcerate progressively, involving > 90% of his body surface, accompanied by high fever, normal C-reactive protein, but highly elevated serum levels of tumour necrosis factor (TNF)-α. Methotrexate 10 mg m−2 weekly was required to halt disease progression, while oral steroids (initial dose 2·8 mg kg−1 daily) alone proved insufficient. Sequential histology revealed progressively dense perivascular and intramural lymphocytic inflammation as well as keratinocyte necrosis. Our case demonstrates the clinical and histological continuum between ‘classical’ PLEVA and FUMHD and points to the potentially pathogenic significance of TNF-α. We hypothesize that in future cases, treatment with TNF-α antagonists might represent a reasonable alternative to high-dose immunosuppressive therapy.