Renal cortical retention (RCR) of contrast medium discovered by delayed X-ray examination is sometimes reported in patients with problems in the urinary system. However, we frequently found RCR even in patients with normal renal function. Therefore, we examined the incidence and factors involved in RCR by delayed computed tomography (CT) 12-24 hours after angiography in 168 patients. RCR was found in 80 of 168 cases (48%). Ioxaglate (60%) and iohexol (60%) showed higher incidences of RCR than diatrizoate (37%) and iopamidol (37%). Multivariate logistic regression analysis was performed to determine the predisposing factors of RCR. Dose of administered contrast medium by body weight (p = 0.004), age (p = 0.009), sex (p = 0.013), type of contrast medium (p = 0.003), serum albumin (p = 0.011), and serum creatinine (p = 0.002) were identified as significant and independent predisposing factors of RCR. We suggest that RCR is not a rare phenomenon if delayed CT is carried out.