OBJECTIVE: The purpose of this study was to assess whether transperineal sonography is valid and accurate for discriminating the low (translevator) type of imperforate anus from the intermediate and high (supralevator) types. The distinction is critical in determination of the surgical approach. MATERIALS AND METHODS: Fifty-six consecutively enrolled infants (0-90 days old) with imperforate anus underwent transperineal gray-scale sonography with a 12-MHz linear array transducer. The distance between the distal rectal pouch and the perineum was measured, and a cutoff distance for differentiating types of imperforate anus was identified. The sonographic findings were compared with the final diagnosis reached with radiographic and surgical findings. RESULTS: Transperineal sonography was feasible in all children without specific preparation. The mean distance between the distal rectal pouch and the perineum in the 22 infants with low imperforate anus was 10 +/- 4 (SD) mm compared with a mean of 24 +/- 6 mm in the 34 infants with intermediate or high anomalies (p < 0.001). The sensitivity of transperineal sonography was 100%; all 34 cases of intermediate or high imperforate anus were identified with a cutoff distance between the distal rectal pouch and the perineum of 15 mm. The specificity of sonography was 86% and the accuracy, 95%. CONCLUSION: Transperineal sonography is a valid and accurate noninvasive imaging technique for differentiating low and intermediate or high imperforate anus.