Adequate therapy of obstructed defecation (pelvic outlet obstruction) is often challenging, as the etiology and clinical symptoms include a wide range of disorders. Standardized diagnostic assessment has to differentiate between obstructed defecation caused by either pelvic outlet obstruction or slow transit constipation. Additionally, morphologic changes of colon, rectum, or the pelvic floor have to be separated from functional disorders. Providing defecography or dynamic MR of the pelvic floor, common causes of outlet obstruction such as sigmoidoceles, in which surgery is indicated, and rectal prolapse can be diagnosed with high accuracy. However, the diagnosis and therapeutic options in symptomatic rectocele and intussusception are controversial. Patients with functional disorders such as rectoanal dyssynergia are candidates for conservative treatment (biofeedback). To identify patients who will benefit from surgery for obstructed defecation, careful patient selection remains the crucial issue in diagnostic assessment.