This report describes the case of a 76 year old man who suffered from febrile ulceronecrotic Mucha-Habermann disease (FUMHD). Despite this patient's typical clinical and histological findings, the fulminating course led to death. Polymerase chain reaction (PCR) analysis of the skin lesions showed that the infiltrating cells were monoclonal in origin and were from an aberrant clone. FUMHD is a very rare, febrile variant type of pityriasis lichenoides et varioliformis acuta, and is characterised by necrotic cutaneous ulcerations associated with high fever and systemic manifestations. Including this present case, only 18 cases of FUMHD have been reported. FUMHD can occur in both adults and children, although there are several differences between the manifestations of the disease in the two groups. One major difference is prognosis: all cases resulting in fatality are of the adult type, whereas no fatal cases have been reported among children. The aberrant clone detected by PCR may be responsible for host responses, resulting in the severe symptoms observed in this disorder.