Psoriasis is a skin disorder that is associated with arthritis. Sacroiliac joint involvement is considered to be less frequent than the other types of psoriatic arthritis. Additionally, the psoriatic sacroiliitis is considered to be asymmetric in general. We aimed to define the frequency and type of sacroiliac involvement in patients with psoriasis. Patients with psoriasis were included the study. Characteristics of skin, nail and articular involvement were noted. Psoriasis area and severity index was calculated. Antero-posterior pelvic X-rays were obtained and graded by two rheumatologists and a radiologist independently. One hundred and thirty-three patients were included. Thirty-seven of patients (27%) have articular involvement symptomatically. The sacroiliac joint involvement was observed in 34 (26%) of patients. More than one-half of sacroiliac involvement was bilateral while less than one-half was in symptomatic patients regarding sacroiliitis. Fifty-seven percentages of all patients have psoriatic nail involvement. Sacroiliac joint involvement did not show any significant association with psoriatic nail involvement or the severity of skin disease. We found higher frequency of sacroiliac joint involvement and bilateral sacroiliitis in patients with psoriasis. This is in contrast to present information about the association of psoriasis and sacroiliitis. These findings need confirmation by further studies and with more sophisticated techniques such as magnetic resonance imaging.