Lateral radiographs of the rectum and anus were taken in 90 children with chronic idiopathic constipation. A computer program was developed to obtain an objective quantitative assessment of the anorectal angle; it averaged 120 degrees at rest, decreased during forceful anal contraction and increased during defecation. It was noted that 24% of the children, when asked to defecate, decreased their anorectal angle as normally observed during forceful anal contraction and, that 21% when asked to contract the anus, increased the angle as if they were defecating. This 'sphincteric disobedience' is probably of major clinical relevance to an understanding of the symptoms of these patients.