The Capillary characteristics of the nail fold area were examined and compared by capillary microscopy in 31 patients with psoriasis (PS) and 34 patients with psoriatic arthritis (PA). 70 healthy persons served as controls. Significantly shorter mean capillary loop lengths and characteristic morphological capillary changes were found both in patients with PS and in patients with PA as compared to the controls. The number of hemorrhages and sluggishness of blood flow was more pronounced in both groups of patients as compared to the control group, but only significantly so in patients with PA. The only significant difference between the PS and the PA groups was a higher subpapillary plexus visibility (SPV) index in the latter. It is concluded that most of the capillary changes demonstrable in patients with PA are clinical manifestations of PS. The difference in the SPV index, however, warrants a follow-up study to elucidate whether patients with PS and a high SPV index are likely to develop arthritis.