Wells' syndrome is a distinctive dermatosis clinically resembling acute cellulitis with solid edema; it resolves spontaneously after weeks or months without residues. Recurrences over many years are common. Light microscopy is characteristic for the disease, with diffuse tissue eosinophilia and marked edema, fibrinoid "flame figures," and palisading microgranuloma. Vasculitis is never found. Eosinophilia of the peripheral blood is a frequent feature. Etiology and pathogenesis are unknown, but the disease has been found to be associated with hematologic disorders in several cases, and recurrences can often be related to infections, arthropod bites, drug administration, or surgery. The diagnosis of Wells' syndrome should be based on the typical clinical picture and the course of the disease with its recurrences and histopathology. Flame figures in histologic sections are an important diagnostic feature but not diagnostic per se for the disease because they represent a reaction pattern that can occur in other conditions. A dilution of Wells' syndrome by making flame figures the central criterion of diagnosis and by lumping all flame figure-positive skin reactions together is therefore unjustified.