Eighty-four patients with long-standing Raynaud's phenomenon (RP) were evaluated by nailfold capillary microscopy (NCM) in a cross-sectional and longitudinal study. The patients were classified in five diagnostic groups: primary familial RP (n = 16), primary nonfamilial RP (n = 20), possible scleroderma (n = 27), scleroderma (n = 16), and the CREST (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia) syndrome (n = 8). In the cross-sectional study, NCM showed gradually decreasing numbers of capillary loops and increasing numbers of widened and giant loops in the following order: primary RP, possible scleroderma, and scleroderma/CREST, suggesting that these diseases are part of a continuing spectrum of RP. In the longitudinal study there was a decrease in the total number of nailfold capillary loops in scleroderma/CREST but not in primary RP and possible scleroderma.