Nailfold capillary patterns were systematically evaluated in 51 controls and 107 patients with Raynaud's phenomenon (RP) by 2 observers. Fifty patients had primary RP, 18 RP with minor signs of connective tissue disease, and 39 secondary RP (scleroderma, CREST syndrome or mixed connective tissue disease [MCTD]). Nailfolds of all 10 fingers were photographed and blindly evaluated. Qualitative and quantitative scoring of patterns was reproducible. The 4th finger showed the fewest nonevaluable photomicrographs and best distinguished primary from secondary RP. Capillary morphology in primary RP did not differ from controls. A decrease in capillary loops best distinguished primary from secondary RP. Addition of the scores for bushy patterns, extravasates, or giant loops led to better discrimination. No item allowed distinction between different connective tissue diseases. The number of enlarged loops was inversely related to the total number of capillary loops (r = 0.55; p less than 0.01).