Vascular involvement is seldom reported in ankylosing spondylitis (AS). In this study, microcirculation was evaluated by nailfold capillaroscopy in 32 defined AS patients compared to a control group (C) of 14 sciatica. Capillary findings were divided into five groups: normal, minor dystrophies, edema, microangiopathy, stagnation. Capillaroscopic abnormalities were more frequent in SA as compared to C, for edema (40% vs 7%) and microangiopathy (15% vs 0%). P = 0.01. There were neither clinical nor biological differences between AS patients with and without microangiopathy. Capillaroscopy abnormalities seem frequent in AS and may be secondary to an immune complex mechanism.