This is a rare autosomal recessive disorder of unknown pathogenesis that almost exclusively affects people of Mediterranean ancestry, especially Sephardic Jews, Armenians, Turks, and Arabs. Patients lack a protease in serosal fluids that normally inactivates interleukin-8 and the chemotactic complement factor 5A. Symptoms present in most patients before the age of 20 years. It is characterized by episodic bouts of acute peritonitis that may be associated with serositis involving the joints and pleura. Peritoneal attacks are marked by the sudden onset of fever, severe abdominal pain, and abdominal tenderness with guarding or rebound tenderness. If left untreated, attacks resolve within 24–48 hours. Because symptoms resemble those of surgical peritonitis, patients may undergo unnecessary exploratory laparotomy. Colchicine, 0.6 mg orally two or three times daily, has been shown to decrease the frequency and severity of attacks. Secondary amyloidosis (AA protein) with renal or hepatic involvement may occur in 25% of cases and is the main cause of death. Colchicine prevents or arrests further progression of amyloidosis development. In the absence of amyloidosis, the prognosis is excellent. The diagnosis of familial Mediterranean fever still is based on clinical criteria. Although the gene responsible for familial Mediterranean fever (MEFV) has been identified, commercial genetic tests fail to identify one of the known gene mutations in up to one-third of patients. Genetic testing is most useful to confirm the diagnosis in patients with atypical symptoms.