The aim of the study was to measure nailfold capillary dimensions and capillary density in patients with primary Raynaud's phenomenon (PRP) and systemic sclerosis (SSc) compared to control subjects. Ten controls, nine patients with PRP and 10 patients with SSc were studied. All dimensions other than distance between limbs were significantly increased in both the PRP and SSc groups compared to controls (P < 0.01), with the SSc group showing the most marked increases (SSc vs PRP, P < 0.05 for all dimensions). Capillary density was significantly reduced in the SSc group compared to controls (P = 0.004). These results suggest that structural vascular changes occur in PRP as well as in SSc, and that PRP may, therefore, not be entirely benign.