Objectives The authors sought to compare the radiation dose between radial and femoral access. Background Small trials have shown an increase in the radiation dose with radial compared with femoral access, but many were performed during the operators' learning curve of radial access. Methods Patients were randomized to radial or femoral access, as a part of the RIVAL (RadIal Vs. femorAL) trial (N = 7,021). Fluoroscopy time was prospectively collected in 5740 patients and radiation dose quantified as air kerma in 1,445 patients and dose-area product (DAP) in 2,255 patients. Results Median fluoroscopy time was higher with radial versus femoral access (9.3 vs. 8.0 min, p < 0.001). Median air kerma was nominally higher with radial versus femoral access (1,046 vs. 930 mGy, respectively, p = 0.051). Median DAP was not different between radial and femoral access (52.8 Gy-cm2 vs. 51.2 Gy·cm2 , p = 0.83). When results are stratified according to procedural volume, air kerma was increased only in the lowest tertile of radial volume centers (low 1,425 vs. 1,045 mGy, p = 0.002; middle 987 vs. 958 mGy, p = 0.597; high 652 vs. 621 mGy, p = 0.403, interaction p = 0.026). Multivariable regression showed procedural volume was the greatest independent predictor of lower air kerma dose (ratio of geometric means 0.55; 95% confidence interval 0.49 to 0.61 for highest-volume radial centers). Conclusions Radiation dose as measured by air kerma was nominally higher with radial versus femoral access, but differences were present only in lower-volume centers and operators. High-volume centers have the lowest radiation dose irrespective of which access site approach that they use. (A Trial of Trans-radial Versus Trans-femoral Percutaneous Coronary Intervention (PCI) Access Site Approach in Patients With Unstable Angina or Myocardial Infarction Managed With an Invasive Strategy RIVAL; NCT01014273 )