The objective of this study was to evaluate the long-term follow-up of patients with Raynaud's phenomenon (RP) and pathological nailfold capillaroscopy (NC) in order to analyse the predictive value of specific features of capillaroscopy for the development of a connective tissue disease (CTD). From 1992 to 2002, NC alone or combined with fluorescence videomicroscopy with sodium fluorescein (NaF) was performed in 1024 consecutive patients because of RP. We analysed the follow-up and pathological features of NC in all patients who had neither clinical nor serological signs of a CTD at the time of NC. Of 308 patients with neither serological findings nor clinical signs of CTD but with RP and pathological features in NC suspicious for CTD, follow-up data were available for 133 patients. An additional NaF test had been performed in 51 (38.4%) patients. After a mean follow-up of 6.5 years (range: 1-15 years), 109 patients had developed a CTD and 24 patients did not show any clinical signs or serological markers for a CTD after a mean follow-up of 8.5 years (range: 2-15 years). There were no differences in age, duration of RP or of follow-up in patients who developed a CTD compared to patients who did not. Significantly more giant capillaries (p=0.0001), avascular fields (p=0.02) and irregular architecture (p=0.0001) had been observed in patients who had developed a CTD during the follow-up of 6.5 years. The presence of giant capillaries, avascular fields and irregular architecture of nailfold capillaries is predictive for the development of a CTD in patients with RP.