Background: Familial Mediterranean fever (FMF) is an autosomal recessive disease that tends to affect certain ethnic groups. It is characterized by recurrent, self-limited attacks of peritonitis, pleuritis, and synovitis. Erysipelas-like erythema (ELE) is the pathognomonic skin manifestation. Lesions are characterized by tender erythematous plaques, usually located on the lower legs. They may be triggered by physical effort and subside spontaneously within 48 to 72 hours of bed rest. Fever and leukocytosis may accompany this condition. Objective: The purpose of this study was to describe the histology and the immunofluorescence findings in ELE and to discuss these observations in relation to the clinical findings in FMF. Methods: We studied 7 patients with FMF in whom ELE developed. In all patients a biopsy was performed within 18 hours from onset of the lesion. In addition to routine hematoxylin and eosin stains, immunohistochemistry to evaluate the infiltrate and direct immunofluorescence were performed. Patients were followed up for their ELE lesions. Results: Histologic examination revealed edema of the superficial dermis and sparse perivascular infiltrate composed of a few lymphocytes, neutrophils, and nuclear dust. Vasculitis was not observed. Direct immunofluorescence showed, in all cases, deposits of C3 in the wall of the small vessels of the superficial vascular plexus. In some cases fibrinogen and IgM were also observed. Conclusion: These findings are in accordance both with those found previously in the erysipelas-like phenomenon and those in the peritoneum of patients with FMF. The sparse infiltrate and the deposition of C3 also are compatible with the clinical picture of self-resolving lesions of short duration. It also suggests that erysipelas-like erythema belongs to the spectrum of neutrophilic dermatoses and supports a pathogenesis that involves abnormal inhibition of the inflammatory cascade. (J Am Acad Dermatol 2000;42:791-5.)