Background: Transradial catheterization improves clinical outcomes of percutaneous coronary intervention (PCI) compared to the transfemoral catheterization. However, inadequate training and experience, perceived technical difficulty, and potential access site complications have limited widespread use. Methods: Retrograde radial angiography was undergone in 326 patients presenting for a first-time radial procedure. Patient characteristics, radial artery anatomy and diameter, and procedure-related factors were assessed and compared with 244 patients with no radial angiography undergone. Results: Mean age was 62.6 years and 37.5% male. The overall incidence of radial artery anomaly was 41.1% (n=134): tortuous radial artery (22.4%, n=73), radial loop (8.6%, n=28), spasm (2.1%, n=7), brachial loop (3.1%, n=10),early branching (4.29%, n=14), others (arteria lusoria 0.3%, n=1). The diameter of radial artery was 1.99짹0.69 mm, 6 Fr-compatible. Crossover rate was 7.3%, not different to 8.7% of no radial angiography group. Use of hydrophilic guidewire was 10.1%, not different to 11.6% of no radial angiography group. Ad hoc PCI was similar in both groups (26.3% vs. 25.7%, p=0.878). There was no significant difference in fluoroscopy time (8.36 vs. 9.04 min), procedural time (33.2 vs. 34.2 min), and contrast volume (144.2 vs. 151.7 ml), when compared to no radial angiography group. A 6 Fr sheath use rather than 7 Fr for PCI was significantly higher in radial angiography group (90% vs. 22.2%, p<0.0001). Access site complications were lower in radial angiography group (3.4% vs. 6.6%, p=0.070). Conclusion: Routine radial angiography helps to pass wire meticulously to prevent unnoticed bleeding and to use long or big sheath in patients with anomalous or slender radial artery, so that it may reduce access site complications and learning period of transradial catheterization.