Twenty-five female and 23 male consecutive patients hospitalized because of severe psoriasis, and 34 consecutive patients hospitalized because of acute anterior uveitis (AAU) were examined. Twelve of the patients with AAU (35%) and 11 of the patients with psoriasis (23%) had definite sacro-iliitis, which was unilateral in 6 (55%) of the former and in 2 (17%) of the latter. No definite radiographic differences in sacro-iliitis between HLA B27-positive and -negative patients could be detected. The radiographic changes of the dorso-lumbar junction (Th9-L2) related to the diseases, were seen only in HLA B27 positive patients with sacro-iliitis. Scattered lateral syndesmophytes were the commonest paravertebral ossifications in patients with psoriasis, whereas more diffuse and more numerous lateral mixed osteophytes appeared most frequently in AAU patients. Parasyndesmophytes were seen both in patients with psoriasis and in those with AAU. Asymptomatic sacro-iliitis was frequently found in unilateral, psoriatic sacro-iliitis (4 out of 6 patients) but was not restricted to this group. No radiographic indications of aortic valve insufficiency or apical lung fibrosis were found.