To evaluate factors which might contribute to treatment failure in children with chronic constipation and soiling, we evaluated the history, physical findings, defecation dynamics, and anorectal function in 97 patients. We treated them with milk of magnesia, high fibre diet, and bowel training techniques and evaluated outcome at one year when 43% had recovered. Recovery rates were similar for boys and girls. Fifty seven per cent of the patients had not recovered. This group at the outset had more frequent soiling episodes, more severe constipation, were less likely to defecate water filled rectal balloons and to relax the external sphincter during defecation. In general girls had more severe constipation, abdominal pain, and a previous urinary tract infection than boys. Girls were more compliant during treatment and had less frequent soiling episodes at one year. Stepwise logistic regression showed that severe constipation, abnormal contraction of the external sphincter and pelvic floor during attempted defecation, and inability to defecate the 100 ml balloon in less than or equal to 1 min was significantly related to treatment failure. Defecation of smaller balloons, volumes for threshold of rectal sensation, critical volume and rectal contraction, and compliance with treatment could not predict treatment failure.