Our aim was to document the progression of psoriatic arthritis in 126 patients prospectively evaluated for a minimum of 5 years. Clinical and laboratory variables and radiographs of the hands and feet, recorded at first and last assessment, were compared to document change in the degree of joint inflammation and damage. During followup there was a significant increase in the use of a number of therapeutic modalities, in particular, gold, PUVA, retinoids and intraarticular glucocorticoid injections. Evidence of inflammatory arthritis was decreased at last assessment relative to presentation. The rate of progression of joint damage, calculated by the ratio of the number of damaged joints to the duration of arthritis in years, actually decreased during followup from 1.97/year to 0.5/year. Nevertheless the proportion of patients with at least 5 damaged joints doubled from 19 to 41% during the study. Thus, despite active treatment and a reduction in joint inflammation and in rate of damage, psoriatic arthritis may be a progressively deforming arthritis, even during 5 years of followup.