Electromyography (EMG) and measurement of voluntary contraction pressure of the external sphincter muscle were performed in 28 patients, aged 5 to 14 years, to assess the function of the external sphincter after surgical correction of anorectal malformations. Ten normal children, aged 5 to 15 years, served as controls. External sphincter function in patients with high-type anomalies was disturbed in the areas of tonic activity, inflation reflex, and activity during further rectal filling. In patients with low-type or intermediate-type anomalies, function was preserved and was equal to that in normal controls. Phasic activity was observed in patients with all types of anomalies and in normal subjects. Among those with high-type anomalies, the three patients with Kelly's score of less than 2 had voluntary contractions of 20 cmH2O or less. However, the mean voluntary contraction pressures were not significantly different among the three types of anomalies. Therefore, patients with high-type anomalies may acquire compensatory voluntary continence through bowel training.