Nine women with severe chronic constipation who were unable to expel a water-filled rectal balloon underwent posterior division of the puborectalis muscle. Pre-operative concentric needle electromyography and measurement of the anorectal angle at rest and during straining suggested that the puborectalis muscle failed to relax during attempted defaecation in these patients. Two patients reported improvement after surgery and had normal balloon expulsion after operation. However seven patients reported no benefit from surgery and tests of defaecatory function and anorectal angle did not change. Incontinence for solid stool was not reported following puborectalis muscle division although five patients reported incontinence of flatus, liquid stool and mucus.