Obstructed defecation poses a challenging clinical problem and in many patients presenting with this syndrome the underlying pathophysiology cannot be determined. Up to now, attempts to diagnose and treat obstructed defecation (anismus) have focused on the function of the somatic pelvic floor musculature surrounding the anorectum, and concepts such as 'puborectalis paradox' and 'spastic pelvic floor' have gained widespread acceptance despite there being no objective data to support such concepts. New evidence showing that defecation is an integrated process of colonic and rectal emptying suggests that anismus may be much more complex than a simple disorder of the pelvic floor muscles. In a small number of patients obstructed defecation is caused by a more simple mechanism, such as internal sphincter hypertonia or a large rectocele, which is easily corrected surgically. Careful selection of patients for treatment, based on identifying the underlying pathophysiological disorder, is emphasized.