An Irish family with an unusual periodic syndrome is described. Attacks consist of fever with localized myalgia and painful erythema. Other features include abdominal pain and pleurisy, with leucocytosis and a high ESR. The syndrome resembles classical familial Mediterranean fever (FMF) but differs from it in its prompt response to steroids and its autosomal dominant pattern of inheritance. The disease appears to have a benign course and no patient has developed amyloid.