Relationships between clinical features of psoriatic arthritis and HLA antigens were examined in 60 patients. HLA-B locus antigens, Bw38, B17, B27 and possibly Bw39 were significantly increased, while HLA-D and DR specificities were not. Cw6 was not studied. The relative risk for disease was doubled in patients having B27 plus a psoriatic HLA antigen. HLA-Bw38 correlated with young age of onset for psoriasis and arthritis, asymmetrical peripheral involvement, and, along with B27, combined peripheral/axial disease. While B17 was also associated with young onset psoriasis, arthritis onset was later and symmetrical in pattern. Certain clinical subsets of psoriatic arthritis may relate to HLA status, and disease susceptibility appears to lie closer to HLA-B than to HLA-D.