Mutations of the tumor necrosis factor receptor 1 (TNFRSF1A) gene underly susceptibility to a subset of autosomal dominant recurrent fevers (ADRFs). We report on a two-generation six-member Dutch family in which a novel R92P mutation and reduced plasma TNFRSF1A levels were found in all the children, including two who are unaffected. However, only the daughter proband and father exhibited a typical TNF-receptor associated periodic syndrome (TRAPS) phenotype. PCR-RFLP analysis revealed that the mutation was not present in 120 control chromosomes from unaffected Dutch individuals. As this R92P mutation is present in two unaffected carriers it appears to be less penetrant than previously reported TNFRSF1A mutations involving cysteine residues in the extracellular domains.