Generalized vitiligo is an acquired, multifactorial, polygenic disease in which depigmented spots of skin, overlying hair, and mucus membranes result from autoimmune-mediated loss of melanocytes from affected areas. We examined single-nucleotide polymorphisms (SNPs) in the PTPN22 and CTLA4 genes in 126 Caucasian families with multiple cases of generalized vitiligo and associated autoimmune diseases, using a family-based association study design. The PTPN22 1858T allele of SNP rs2476601 is significantly associated both with generalized vitiligo and with an expanded autoimmunity phenotype. Individuals carrying the PTPN22 1858T allele had an allelic odds ratio (OR) of 2.16 for generalized vitiligo and a genotypic OR of 2.35 as C/T heterozygotes. Similarly, individuals carrying the PTPN22 1858T allele had an allelic OR of 2.05 for the expanded autoimmunity phenotype, and a genotypic OR of 2.19 for C/T heterozygotes. Examination of five SNPs in the CTLA4 gene (rs1863800, rs231775, rs3087243, rs11571302, rs11571297, rs10932037) in the same 126 families yielded no evidence of allelic or genotypic association with either generalized vitiligo or the expanded autoimmune phenotype. These results implicate PTPN22 in mediating susceptibility to generalized vitiligo and associated autoimmune diseases, but do not support a role for CTLA4.