The aim of this study is to determine the prevalence of psoriatic arthritis (PsA) according to CASPAR criteria, ASAS peripheral and axial SpA criteria, and New York criteria for AS. The first 100 patients consecutively attending a psoriasis dermatology clinic were assessed. Demographic and clinical data were collected; all patients were questioned and examined for joint manifestations. Rheumatoid factor and radiographies of hands, feet, cervical spine, and pelvis for sacroiliac joints were obtained. X-rays were read independently by two experienced observers in blind fashion. Patients with objective joint manifestations, both axial and peripheral, were evaluated for fulfillment of CASPAR, ASAS peripheral and axial, and New York criteria. Median age 48 years; 93 % of patients had psoriasis vulgaris and 56 % nail involvement. Seventeen patients had peripheral arthritis as follows: nine mono/oligoarticular and eight polyarthritis. Median arthritis duration was 8 years. Seventeen percent of patients fulfilled CASPAR and ASAS peripheral criteria, 6 % New York, and 5 % ASAS axial criteria. Patients who met CASPAR criteria showed a significantly higher psoriasis duration compared to those without arthritis (M 16 vs. 10 years, p = 0.02), and a higher frequency of nail involvement (88.2 vs. 49.4 %, p = 0.003). Five patients (29.4 %) fulfilled ASAS axial criteria; all of them had peripheral involvement as follows: mono/oligoarticular in three patients and polyarticular in two. Patients with peripheral and axial involvement presented a significantly higher frequency of erythrodermic psoriasis compared to the other patients (35.3 vs. 1.2 %, p = 0.0006 and 80 vs. 16.7 %, p = 0.02). Prevalence of PsA, for CASPAR and ASAS peripheral criteria, was of 17 %. Five percent of patients met ASAS axial criteria, while 6 % met New York criteria. Worth noting, few patients without signs or symptoms of arthritis had radiological changes, both axial and peripheral, precluding a proper classification.