Linkage in families and association in population case-control investigations have clearly shown that genes within the major histocompatibility complex region on chromosome 6p are relevant to the susceptibility and pathogenesis of ulcerative colitis (UC) and Crohn's disease. However, identifying the causative variants by fine mapping has not been conclusive. In this study using 58 single nucleotide polymorphisms (SNPs) with 616 UC cases, there was significant association with SNP rs2294881 of the (butyrophilin-like 2) BTNL2 gene with odds ratio (OR) = 2.80, confidence interval (CI) = 1.62-4.84 and P = 5.69 x 10(-4) (P(Bonferroni) = 3.3 x 10(-2)) and replication of SNP rs9268480. The missense SNP rs2076523 (K196E) showed novel association with a subset of UC cases with colectomy (n = 126), OR = 0.25, CI = 0.11-0.58 and P = 4.42 x 10(-4) (P(Bonferroni) = 2.56 x 10(-2)). These three associated variants within the BTNL2 gene were neither in linkage disequilibrium with each other nor correlated with the SNPs tagging the human leukocyte antigen (HLA)-DRB1*1502 and HLA-DRB1*0301 alleles.