In this study 56% of children with chronic constipation and encopresis were unable to defecate rectal balloons. Most of them had an abnormal contraction of the external and sphincter during defecation trials. Eighty-six percent were still unable to defecate balloons 1 year later after having complied with a conventional treatment program. Only 14% of patients unable to defecate balloons had recovered by 1 year, whereas 64% of patients able to had recovered (p less than 0.02). Only 13% of patients unable to relax the external sphincter had recovered by 1 year, whereas 70% of those able to do so had recovered (p less than 0.01). In addition, none of the patients with an abdominal fecal mass present during the initial examination independent of ability or inability to defecate balloons had recovered (p less than 0.001). This study shows that abnormal defecation dynamics and the severity of constipation are predictors for persistence of chronic constipation and encopresis.