Changes in the microvasculature are considered to play an important part in the pathogenesis of psoriasis and its associated arthritis. The novel method of nailfold video capillaroscopy is an extension of the technique of widefield nailfold microscopy which has been of diagnostic and predictive use in the in vivo study of the microcirculation in systemic sclerosis and other connective tissue disorders. However, similar studies in patients with psoriasis and psoriatic arthritis and/or nail changes have produced conflicting results. We tested the hypothesis that any abnormalities in nailfold capillaries of either a quantitative or qualitative nature might be observed more readily in subjects with pathology adjacent to the nailfold, i.e. distal interphalangeal (DIP) joint changes and/or nail dystrophy, when using this technique. Forty-four patients with psoriasis were recruited (21 males, 23 females). Twelve patients had psoriasis alone, 13 had psoriasis and nail changes, six had DIP joint involvement with changes of psoriasis elsewhere, and 13 had psoriasis, DIP arthritis and nail changes. Capillary density and standard capillary dimensions were studied and compared with those of 44 age- and sex-matched control subjects. There was a significant (P < 0.05) decrease in capillary loop density in patients with either psoriasis plus nail disease (14.5 +/- 5.7 capillaries per 3 mm field) or psoriasis plus nail and DIP joint disease (14.3 +/- 5. 0) when compared with controls (19.2 +/- 3.8). In patients with psoriatic arthritis affecting the DIP joints, there was a statistically significant (P < 0.05) decrease in arterial and venous capillary limb diameters, and this was also seen in those with arthritis associated with nail changes. However, there was no difference in capillary dimensions between patients with psoriasis and/or nail changes when compared with normal controls. Morphological abnormalities previously described in the literature were not noted in any of our four patient groups. Our findings of diminution in both nailfold capillary bed density and dimensions of the arterial and venous capillary limbs suggest that vascular injury, previously noted in ultrastructural studies, may play a part in the pathogenesis of psoriatic arthritis. However, in contrast to previous studies, we found no specific pattern of a morphological nature of nailfold capillaries in patients with psoriasis with or without nail changes, when compared with normal controls.