The clinical, laboratory, and radiological features, including histocompatibility typing, of 28 patients with juvenile psoriatic arthritis are reported. The most common presentation was that of psoriasis preceding or occurring simultaneously with arthritis. The most common course of juvenile psoriatic arthritis was to start as an oligoarthritis and progress, usually to polyarthritis. No patients with juvenile psoriatic arthritis had uveitis. Overall, most patients had a good outcome (93% in functional class I and II), though 8/28 (29%) did require disease modifying drugs over a mean period of 8.8 years of follow up. The clinical features of these patients were very similar to those of a group of 158 adult patients with psoriatic arthritis with the same disease duration followed up in the clinic. Although there was an increased prevalence of B17 in both juvenile and adult psoriatic arthritis, juvenile psoriatic arthritis showed increased prevalence of A2, whereas adult psoriatic arthritis showed increased prevalence of B27, Bw39, and Cw6. This HLA association differed from that reported in other forms of juvenile arthritis.