Transradial cardiac catheterization (TRCC) has unique technical challenges such as access difficulty related to anatomical variations and/or radial artery (RA) spasm. We sought to evaluate the incidence of anatomical variations of the RA and whether they would affect RA spasm and procedural achievement of TRCC. A total of 744 consecutive patients who underwent TRCC were analyzed by routine radial arteriography. Anatomical variations were defined as abnormal origin of the RA and/or radioulnar loop and/or tortuous configuration. RA spasm was defined as >75 % stenosis at first radial arteriography. Overall, anatomical variations were noted in 68 patients (9.1 %), including 39 cases of abnormal origin (5.2 %), 11 cases of radioulnar loop (1.5 %), and 42 cases of tortuous configuration (5.6 %). Transradial procedures failed in 26 patients (3.5 %), and more frequently in patients with anatomical variation than in those with normal anatomy (23.5 % vs 1.5 %, P < 0.001). Importantly, on multivariate analysis the presence of anatomical variation was a distinct predictor of transradial procedure failure (odds ratio (OR) 17.80; 95 % CI 7.55-43.73; P < 0.001). RA spasm was observed in 83 patients (11.2 %), and more frequently in patients with anatomical variation than in those with normal anatomy (35.3 % vs 8.7 %, P < 0.001). Anatomical variation (OR 4.74; 95 % CI 2.61-8.47; P < 0.001) and female gender (OR 2.23; 95 % CI 1.01-4.73; P = 0.041) were distinct predictors of RA spasm. Anatomical variations were observed in 9.1 % of the patients, and strongly correlated with RA spasm and procedural achievement of TRCC.