Psoriatic arthritis is a chronic destructive joint disease. About 40% of psoriatic arthritis patients are positive for human lymphocyte antigens (HLA)-B27. This study investigated the relationship between HLA-B27 and clinical manifestations and prognosis in psoriatic arthritis patients. Demographic, clinical, and laboratory data were analyzed from 41 psoriatic arthritis patients with regular follow-ups. The mean percentage of HLA-B27 in psoriatic arthritis was about 39%. Positive HLA-B27 was associated with an increased risk of development of sacroillitis (relative risk 8.75; p<0.01) but not peripheral arthritis (p=0.925). Psoriatic arthritis patients with psoriatic nail disease (41.5% vs 2.4%, p<0.01) and distal interphalangeal joints involvement (26.8% vs 3.4%, p<0.05) had significantly increased risk of developing deformed joints. Psoriatic arthritis patients with positive HLA-B27 tend to develop deformed joints (p=0.068) as well as having elevated levels of C-reactive protein (p=0.072), although these results did not attain significance. HLA-B27 antigen may serve as a useful predictive marker for the development of sacroiliitis in Taiwan.