Evaluation of the sacrum in anorectal malformations (ARMs) is important because of the frequent association with ARMs and functional outcome after correction of ARMs. Sacral defects are not easily detected because of immaturity of sacrum in children and overlooking of pediatric surgeons. The authors utilized the sacral ratio in normal children and patients with ARMs. In normal children, the mean true sacral ratio and mean sacrococcygeal ratio were 0.60±0.08 and 0.72±0.13 respectively. Sacral ratio was not correlated with age and did not changed with age in 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.