It is well known that genetic heterogeneity and/or the complex interaction of several MCH-linked risk factors can explain the onset and the broad spectrum of Psoriatic Arthritis (PsA) from the clinical point of view. Fifty-eight patients with PsA (Moll and Wright criteria), 35 men and 23 women, mean age of 45, 14, were studied; all the patients were assessed by both clinical and radiological examination, with particular attention to the sacroiliac joints. HLA typing of the patients confirmed the association between PsA and HLA-B39 (p = 0.0008) and Cw6 (p = 0.0011). In addition a significant increase in DQ2 antigen (p = 0.004) has been found. No correlation of any particular HLA antigen with clinical subsets (oligo-polyarticular peripheral PsA, axial PsA and axial with peripheral PsA) or erosive incidence of joint involvement-generally related to the duration of the disease--was found.