Feedback control has been postulated to improve the efficacy of laser welding in microsurgery, but alteration of outcome has not been clearly shown. The authors evaluated the ability of an optical closed loop temperature feedback control to improve patency, aneurysm rate, and to histologically limit thermal damage. Rat femoral artery anastomoses were performed under operating microscope magnification. One hundred and twenty-four anastomoses were performed in five groups using 1) free-hand (FH) 1.9-microm laser soldering without feedback; 2) temperature controlled (TC) 1.9-microm laser soldering with optical feedback; 3) FH 808 nm laser; 4) TC 808 nm laser soldering; and 5) 10-0 nylon suture control. In Groups 2 and 4, an optical feedback system controlling laser exposure to produce a preset temperature was used. Anastomotic time was significantly less for all laser groups (p < 0.05). Late patency for all 1.9-microm laser anastomoses was almost 0. Temperature controlled 808-nm anastomoses showed no significant difference from sutures in terms of patency (88 percent vs. 96 percent), bursting pressure, and aneurysm rate, while freehand 808-nm anastomoses had a significantly lower patency (71 percent) and more tissue damage (ANOVA, p < 0.05). The authors conclude that temperature control improves outcome in microvascular anastomosis by reducing transmural thermal injury caused by variations in surgeon technique.