The current knowledge of the relationship between the HLA system and the different forms of Juvenile Chronic Arthritis is reviewed: Of the different forms the Early Onset Pauciarticular JCA is associated with DRw8, DR5 and A2, the Polyarticular Onset Rheumatoid Factor positive JCA shows the same pattern of association as does the Adult Rheumatoid Arthritis namely with DR4 and DR1. Juvenile Spondylitis is strongly related to the presence of B27. For the other clinical forms of Juvenile Chronic arthritis the data are not sufficiently well established to give a definite association. In Early Onset Pauciarticular JCA the association with the DR antigens DRw8 and DR5 is independent of that with HLA-A2. Thus there must be at least two HLA linked regions contributing to susceptibility to this form of JCA, one in the region of HLA-A and the other one in the HLA-DR region. If Early Onset Pauciarticular JCA is analysed according to the type of onset (Monoarticular, with large joints, with large and small joints, with small joints only and with Iridocyclitis) there are no significant differences in the frequencies for the associated DR alleles DR5 and DRw8. The antigen DR4 is not found at all in patients with Monoarticular Onset and in increasing frequencies with the increased number of involved joints. Analysis of the same patients according to the clinical course of the disease (Persistent Pauciarticular, Extended Pauciarticular, Polyarticular) shows that again there are no significant deviations for the associated antigens A2, DR5, DRw8. DR4 is not found in the group with Persistent Pauciarticular Disease.