The authors examined the effect of twisting on the patency of microvascular anastomoses 3 days after surgery. A total of 69 male Wistar rats were divided randomly into four groups. The femoral arteries and veins were dissected for a standard distance. A total of 69 microarteriorrhaphies and 68 microvenorrhaphies were performed at 0 deg and with twist of the vessel ends of 90, 180, and 270 deg. Three-day patency rates for arterial microanastomoses were 100% with a 0-deg twist, 80.9% with a 90-deg twist, 68.4% with a 180-deg twist, and 64.2% with a 270-deg twist. Three-day patency rates for venous microanastomoses were 100% with a 0-deg twist, 85% with a 90-deg twist, 28.5% with a 180-deg twist, and 25% with a 270-deg twist (p = 0.047 for arteries, p = 0.001 for veins). These data are statistically significant. Moreover, assuming the risk of thrombosis to be 1 for microanastomosis without twisting, the odds ratio for the risk of vessel thrombosis for 270-deg twisting (the maximal examined degree of arterial and venous twist in the current study) is 10.08 for arterial anastomosis and 226.85 for venous anastomosis.