The purpose of this study was to find the correlation between intraoperative blood flow and early patency of the radiocephalic fistula. Between March 1998 and March 1999, 50 radiocephalic arteriovenous fistulas were constructed in 41 patients. Intraoperative blood flow measurements were made 10 min after completion of the vascular anastomoses with 3-4 mm handheld flow probes. Patients were followed until failure of fistula or 3 months after the first hemodialysis with these fistulas. Intraoperative blood flow as well as age, gender, presence of diabetes, size of cephalic vein, thrill on the fistula, and flow of radial artery were correlated with early patency. The mean intraoperative blood flow was 174.7 +/- 13.2 mL/min and ranged from 50 to 500 mL/min; it was the only significant parameter that determined early patency of the radiocephalic fistula. Fistulas with flow <160 mL/min (10 of 25) had a higher failure rate than those with flow >160 mL/min (4 of 25), which was statistically significant (p < 0.01). All of the patients with flow <70 mL/min (5 of 5) failed to maintain patency within a month. However, the other variables were not correlated with early patency. We conclude that intraoperative blood flow is a reliable parameter that determines the early patency of radiocephalic fistulas.