['To quantify earlier capillary diameter abnormalities, observed by nailfold videocapillaroscopy (NVC), in primary Raynaud phenomenon (PRP) subjects compared with RP subjects later evolved to systemic sclerosis (SSc)-associated secondary Raynaud phenomenon (SRP).', 'There were 6112 NVC images of 191 subjects analyzed at baseline and after a mean followup of 42.77 ± 35.80 months. We selected 48 patients affected by SRP and 143 matched controls confirmed with PRP. The diameter of the most dilated limbs (arterial, venous, and apical) was measured in 16 images per subject. Statistical analysis was performed using nonparametric tests. The threshold values for capillary diameters associated with the development of SSc-associated SRP were determined through receiver-operating characteristic curves.', 'Mean capillary diameter values were significantly different for arterial, venous, and average diameters (mean value of arterial, venous, and apical) between patients with PRP and SRP (p < 0.0001). These alterations were found to be independent predictors for disease development (p = 0.015). Threshold values of 30 µm (area under the curve = 0.802, sensitivity/specificity = 0.85/0.63) to 31 µm were identified for average, arterial, and venous diameters, with a shortening effect on time to disease development.'] Do quantitative Alterations of Capillary Diameter Have a Predictive Value for Development of the Capillaroscopic Systemic Sclerosis Pattern?