Digital skin vasoconstriction on local cooling is exaggerated in primary Raynaud's phenomenon (RP) as compared with controls. A significant part of such vasoconstriction relies on the inhibition of the nitric oxide (NO) pathway. We tested the effect of the phosphodiesterase 5 (PDE5) inhibitor sildenafil, which potentiates the effect of NO, on skin blood flow. We recruited 15 patients with primary RP, performing local cooling without sildenafil (day 1), after a single oral dose of 50 mg (day 2), and after a dose of 100 mg (day 3). Skin blood flow, skin temperature, and arterial pressure were recorded, and data were expressed as cutaneous vascular conductance (CVC). Sildenafil at 100 mg, but not 50 mg, significantly lessened the cooling-induced decrease in CVC. It also increased resting CVC and skin temperature. These data suggest that 100 mg sildenafil improves digital skin perfusion during local cooling in primary RP. The benefit of sildenafil "as required" should be confirmed in a randomized, controlled trial.