Autoimmune diseases and autoantibodies have been documented in 42 index cases with definite primary Sjögren's syndrome (1 degree SS), 207 relatives and 39 spouses. The results were compared with control data from a local population survey. Thyroid disease, 1 degree SS and their associated autoantibodies were the commonest autoimmune abnormalities observed and found predominantly in older female relatives. The HLA-DR3 phenotype associated with 1 degree SS, antinuclear factor, hypothyroidism, and thyroid microsomal antibody. Rheumatoid arthritis and systemic lupus erythematosus were not found in excess in the families. Primary Sjögren's syndrome is frequently associated with thyroid disease and we suggest that there is a common genetic predisposition between these diseases which differs from 2 degrees SS associated with rheumatoid arthritis and systemic lupus erythematosus. This includes MHC and non-MHC genes.