Nailfold capillaries may be visualized in vivo using a simple non invasive microscopic technic. The assessment of capillary flow disturbances and organic microangiopathies is therefore rendered possible through capillary microscopy. Three kinds of clinically significant morphological abnormalities can be easily recognized: megacapillaries are huge capillaries with a diameter greater than 50 microns. They are mainly found in progressive systemic sclerosis and dermatomyositis, together with avascular areas and pericapillary edema; ramified capillaries are neovessels, most frequently related to subclinical cutaneous vasculitis; capillary hemorrhages may be induced either by active microangiopathies, or by deep vasomotor changes. The semiological consistency of these abnormalities makes capillary microscopy a valuable procedure for the early recognition of connective tissue diseases and the evaluation of vasomotor disturbancies in children as well as in adults. Further investigation of other microangiopathies like purpura rheumatica and diabetes are needed.