Eighty-seven patients diagnosed as having primary Raynaud's phenomenon (Raynaud's disease) were reexamined after this symptom had been present for a mean of 8.8 years (range 2.0–34.5). One or more additional clinical feature(s) suggesting an underlying connective tissue disease were found in 12 patients (14%) at first evaluation, and in 23 (26%) by the last evaluation. The most frequent findings were puffy fingers (10 patients), digital tip pitting scars (8 patients), and digital tip ulcerations (6 patients). Distal esophageal hypomotility and/or decreased pulmonary diffusing capacity for carbon monoxide were found in 12 patients. Only 4 individuals (5%) developed clear evidence of a connective tissue disease, and in all cases, the diagnosis was the CREST (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasias) syndrome variant of systemic sclerosis. This condition became obvious 8–17 years after the onset of Raynaud's phenomenon. One or more serologic test values were initially abnormal in 2 of these CREST syndrome patients, as well as in 12 patients who continued to have primary Raynaud's phenomenon at the last evaluation. The combination of puffy fingers, digital pitting scars, and serum anticentromere antibody, all consistent with CREST syndrome, occurred in a small group of patients. None of the 78 patients whose serologic tests were repeated during followup had a change in the serologic profile. These results suggest that only a small proportion of patients with primary Raynaud's phenomenon develop one of the connective tissue diseases during the first decade after onset. When such a disorder does appear, systemic sclerosis with the CREST syndrome variant is the most likely eventual diagnosis.