We describe 2 Dutch patients with recurrent fever attacks undiagnosed for more than 40 years. The diagnosis of periodic fever was made when molecular analysis revealed novel mutations in the tumor necrosis factor (TNF) receptor gene (TNFRSF1A), establishing the diagnosis of TNF receptor–associated periodic syndrome. This syndrome is an autosomal dominant disorder characterized by recurring episodes of fever, arthralgia, and skin lesions that is caused by mutations in the 55-kd TNFRSF1A gene. This finding has facilitated treatment for TNF receptor–associated periodic syndrome because blocking of TNF signaling seems to alleviate the symptoms. Use of a short course of recombinant p75TNFR:Fc fusion protein (etanercept) induced prolonged remission in one patient.