To determine the hereditary pattern of acute anterior uveitis (AAU) 12 families with 2 cases of AAU in each family were given a routine eye examination which included serological determination of HLA antigens. Members of four families underwent x-ray examination of the lumbosacral spine. Of the 23 cases with AAU examined, 19 had the antigen B27. The genes determining B27 and a2 were inherited together in 14 instances and the gene determining Cwl in 10 of these 14. The lymphocytes of the HLA identical siblings of the three families studied by the mixed lymphocyte culture test did not react against each other. Sacroilities was seen in 62.5% of cases with familial AAU and in 58.6% of their relatives. It is concluded that HLA-B27 is linked with genes predisposing the carrier to familial AAU, which is closely related to the rheumatic group of diseases.