The presence of sacroiliitis was studied in 100 consecutive psoriatic patients, 62 males and 38 females. In this selected population 14 patients (14%) had grade 2 to 4 sacroiliitis, in seven associated with clinical findings of ankylosing spondylitis (AS). Sacroiliac joint involvement was significantly related to more severe cutaneous and ungual psoriatic disease. Sacroiliitis was observed in nine males and five females but clinical AS predominated in the males, six males and one female. No difference in distribution was observed by sex, onset age, or duration of psoriasis when patients with and without sacroiliitis were compared. However, patients with sacroiliitis more frequently had peripheral joint involvement.