Indications for nailbed capillaroscopy in Raynaud's phenomenon

175 patients with Raynaud's phenomenon underwent nailfold capillaroscopy. 22 had suspected connective tissue diseases, 48 idiopathic Raynaud's disease and 105 a variety of other diagnoses. A normal capillaroscopy is fully consistent with Raynaud's disease. A pathological capillaroscopy with megacapillaries prompts suspicion of underlying connective tissue disease. The other abnormal capillaroscopies are suggestive of Raynaud's phenomenon secondary to one of the numerous associated diseases, and do not rule out evolution to connective disease ("waiting group"). The proposed simplified classification seems to offer reasonably good discrimination. The probability of an abnormal capillaroscopy increases with the age of onset of Raynaud's phenomenon but is not insignificant in younger patients. The (53-year-old) Allen's criterion (3 years follow-up without signs of underlying diseases such as scleroderma, etc.) is disappointing and should be discarded. Nailfold capillaroscopy is a non-invasive procedure which is useful at any age.