Nailfold capillaries in 28 patients with OA affecting the distal interphalangeal joints were compared to 23 age- and sex-matched controls without OA. Patients with OA showed a significantly lower density of capillaries in their nailfolds and significantly more capillary morphological abnormalities including haemorrhage, 'drop out', dilatation and irregularity. There was a trend for OA patients to have warmer fingers with reduced finger to brachial blood pressure ratios. There were significant correlations between nailfold capillary numbers and average joint tenderness and between capillary morphological changes and joint swelling. These results reveal a relationship between interphalangeal joint OA and nailfold capillary abnormalities and density. As changes in microcirculation may be pertinent to the pathogenesis of OA, further studies which could explore possible causal relationships are warranted.