We carried out a prospective study of the clinical, laboratory and radiological features of 180 patients with psoriatic arthritis. We initially classified our patients into five groups as described in the publications of Moll and Wright. Thirty-seven per cent had oligoarthritis, 36% polyarthritis, 23% spondarthritis (sacroiliitis and/or spondylitis) and 4% had the mutilans form. The distal joint arthritis type did not exist as an entity and the distal interphalangeal (DIP) joints were affected in all groups. The spondarthritis form includes patients with exclusively axial manifestations and also those who in addition have peripheral arthritis (oligoarthritis, polyarthritis, DIP arthritis). Only 53% of our patients had nail involvement. We found an increase of IgA levels in patients with axial disease. This suggests a relationship between ankylosing spondylitis and psoriatic spondylitis. The HLA-B17/Cw6 association increased in the oligoarticular form. The increase of antigen B17 correlated with the spondarthritic and oligoarthritis forms whereas Cw6 was more important in the oligoarthritis form. An increase of the HLA-B27/Cw1 association and the spondarthritic form was also found. Moreover, we detected a greater incidence of the HLA-B27 antigen in patients with bilateral sacroiliitis (85%) than in patients with unilateral sacroiliitis (22%). Our work revealed that PA is not a harmless disease; 57% of our patients had erosive arthritis while 19% had ARA class III or IV functional impairment.