Evaluation of the sacrum in anorectal malformations (ARMs) is important because there is an association between sacral abnormalities and poor functional outcome after corrective surgery for ARM. Sacral defects are not easily detected because of immaturity of sacrum in children and defects are often overlooked by pediatric surgeons. The authors utilized the sacral ratio in normal children (N=61) and patients with ARMs (N=26). In normal children, the mean true sacral ratio and mean sacrococcygeal ratio were $0.60{pm}0.08$ and $0.72{pm}0.13$ respectively. The sacral ratio was not correlated with age and did not changed with age in the same patient. However, true sacral ratio and sacrococcygeal ratio were significantly lower in patients with high type ARMs than those of normal children (p<0.001). There was no difference between patients with low type ARMs and normal children. These results suggest that abnormal sacrums are more frequently encountered in patients with high type ARMs than in normal children, and that true sacral ratio and sacrococcygeal ratio can be used in the evaluation of the abnormal sacrum.