Nailed capillaroscopy was systematically performed in 30 patients with Behcet's disease to search capillary dystrophies with paradoxal normal number of capillary loops; some indirect signs of microvascular disease were noted: pallor of the background; petechiae; sludge; abnormal visibility of the venous plexus and of irregularly arranged venules. Eight patients had a normal capillaroscopy: thirteen had direct signs of microvalvular abnormalities (nine cases with two direct signs and at least two indirect signs; and four cases with two direct and one indirect, or one direct and three indirect signs). Nine patients had only sludge and/or petechiae. We never observed any abnormality in the number of the capillaries, in the sweat droplets nor in the circulatory speed. Two patients had megacapillaries resembling those seen in scleroderma. The petechiae were observed in 50 p. 100 of the cases. We found no correlation between the capillaroscopic abnormalities and the age, sex, duration of the disease, or ethnic background. However, the presence of aphthosis the day of the capillaroscopy seems to be correlated with the cutaneous microvascular abnormalities. Thus, there exist frequent capillaroscopic abnormalities in Behcet's disease. Although aspecific, they point out the vascular tropism of this disease, resembling that of the vascularite. The prognostic importance of the capillaroscopy in Behcet's disease is under study.