Systemic sclerosis (SSc; scleroderma) is a connective tissue disease, characterized by fibrotic, immunological, and vascular abnormalities. Interleukin-10 (IL-10) is an anti-inflammatory cytokine that modulates collagen production and B-cell survival. To determine if certain IL-10 genotypes are risk factors for the development of SSc and influence disease-associated autoimmune responses, 248 Caucasian and 264 Japanese SSc patients and controls were genotyped for three loci: -3575, -2849, and -2763. Sera from patients were characterized for SSc-associated autoantibodies. In Caucasians, at -3575 and -2763, the frequency of AA homozygotes was higher in patients as compared with controls (P=0.0005; P=0.002). In Japanese subjects, the frequency of AC heterozygotes at -2763 was higher, and that of CC homozygotes lower, in patients with diffuse SSc as compared to controls (P=0.04). Particular IL-10 genotypes were associated with SSc-related autoantibodies. These results suggest that IL-10 genotypes contribute to the etiology of scleroderma.