To assess the prognostic value of scleroderma pattern of nailfold capillary changes for the development of connective tissue diseases (CTD) in subjects with primary Raynaud's phenomenon (RP). The study included 3,029 consecutive patients with primary RP who had been followed at 6-month intervals during the mean of 4.8 years. The pathological features of nailfold capillaroscopy were recorded in all patients who had neither clinical nor serological signs of a CTD. In patients who developed CTD, capillary changes obtained 6 months prior to diagnosis were analyzed. A possible relationship between capillary changes and the presence of associated CTD was assessed. At the end of follow-up, 1,660 (54,8%) patients have still the primary RP, 246 (8,1%) had suspected secondary RP, and 1,123 (37,1%) patients developed CTD (363 undifferentiated CTD, 263 systemic sclerosis, 143 systemic lupus erythematosus, 106 rheumatoid arthritis, 102 Sjögren's syndrome, 61 overlap syndrome, 30 vasculitides, 24 mixed CTD, 19 polymyositis, 7 dermatomyositis, and 5 primary antiphospholipid syndrome). Scleroderma pattern were significantly associated with the development of systemic sclerosis [P = .00001, sensitivity 94%, specificity 92%, positive predictive value 52%, negative predictive value 99%, and odds ratio 163 (95% CI, 97,9-271,5)], as well as dermatomyositis (P = .0004), overlap syndrome with signs of systemic sclerosis (P = .0001), and mixed connective tissue disease (P = .007). Capillary microscopy is effective method for differentiation between primary and secondary RP and useful tool for the prediction of scleroderma spectrum disorders in RP patients.