Juvenile idiopathic arthritis (JIA) is a complex genetic disease of autoimmune etiology. Fas is a molecule with a pivotal role in apoptosis and hence in immune regulation. Elevated transcriptional levels of Fas in the synovial fluid of patients with JIA suggest that it might be implicated in disease etiopathogenesis. We investigated whether a polymorphism in the Fas promoter region (-670) confers susceptibility to JIA.In this association study, 342 UK patients with JIA and 255 healthy individuals were genotyped for the polymorphism using polymerase chain reaction restriction fragment length polymorphism. Comparisons of the genotypic frequencies were made using chi-square analysis.No statistically significant differences were found when the genotype frequencies of the -670 Fas polymorphism were compared between the JIA cases and the control panel. Similarly, no differences were seen between the JIA subgroups, or when the patients were divided on the basis of rheumatoid factor or antinuclear antibody positivity.The -670 polymorphism of Fas does not appear to be associated with susceptibility to JIA.