Our aim was to test the reliability of clinical measurements in psoriatic arthritis. The study involved clinical assessments of inflammatory activity as well as damage in 10 patients with psoriatic arthritis seen at the psoriatic arthritis clinic. Five rheumatologists examined these patients according to a latin square design. For the clinical measurements of actively inflamed joints and damaged joints there was no significant observer effect. This suggests that these are reliable measurements. There was, however, significant observer effect in the radiologic assessment, and further refinement of the measurement is required.