A pedigree of familial ulcerative colitis with their HLA haplotypes is reported. The mother and two children, the eldest and second of three sons were affected. The mother developed proctitis at age 35, and the lesion extended to the entire colon at the time of a relapse. The two sons developed ulcerative colitis in a similar fashion; total colitis, of moderate severity, developing at age 16 in both. The analysis of HLA haplotypes of all five family members suggested that the HLA responsible for ulcerative colitis in this family was not HLA B, C, or DR, but Aw24 and DQw1. The third son had the same HLA haplotype as the second son, and it was presumed that he would develop ulcerative colitis in the future. These cases, together with other cases of familial ulcerative colitis indicate that Aw24 and DQw1 are critical phenotypes for ulcerative colitis in Japan.