The following four points are discussed in this study: (1) Human leukocyte antigen (HLA) genes are associated with all groups of juvenile rheumatoid arthritis patients to varying degrees. (2) These HLA associations are similar to those of some adult inflammatory arthropathies (rheumatoid arthritis and ankylosing spondylitis), but distinct in others. (3) Predisposition commonly involves a contribution from both of a subject's HLA haplotypes. (4) Unusual immunogenetic aspects include a HLA-DP association, independent of linkage disequilibrium with other class II genes, and a HLA-associated mechanism increasing the relative proportion of girls in the involved sibships.