Behçet's disease (BD) is a multisystem inflammatory disease characterized by recurrent orogenital ulceration, ocular inflammation, and skin lesions. The etiology of the disease is currently unknown but evidence suggests that there is a strong genetic component mediating the chronicity of the disorder. We have examined the association between polymorphisms at position -1082, and -819 in the promoter region of the gene encoding IL-10 in patients with Behçet's disease from two distinct patient populations. The IL-10 -1082AA genotype was weakly associated with BD when all patients were analyzed as a group (pc = 0.04, OR 1.4, 95% CI 1.1-1.9), but not in the UK or Middle Eastern (ME) cohorts of patients alone compared to local controls. An association with IL-10 -819T was evident in all BD patients, (pc = 0.02, OR 1.5, 95% CI 1.1-2.0), and this was because of an association in the UK but not ME patients (pc = 0.0004, OR 2.1, 95% CI 1.4-3.3). The -1082A/-819T haplotype, which is linked to low production of this cytokine, was not significantly associated with Behçet's disease. This link between BD, a chronic, relapsing, autoinflammatory condition, and a genotype associated with low IL-10 production provides evidence that abnormalities in the genetic control of cytokine levels may be relevant in influencing the immune response in Behçet's disease in some patient groups.