Bladder function in the mentally retarded. A group of 21 mentally retarded patients with severe, long-standing urinary symptoms underwent urodynamical investigation. The most common abnormalities were detrusor areflexia and detrusor hyper-reflexia. Of 11 patients treated surgically, 10 derived marked benefit. Drugs were successful in reducing micturition problems in 3/6 patients. Severely retarded patients with spastic quadriplegia are difficult to investigate and if this is associated with detrusor hyper-reflexia it is impossible to treat them in any way. Severely retarded patients with detrusor areflexia and infrequent voiding can benefit from bladder outlet surgery. Patients with moderate (especially mild) retardation can be investigated and treated in the same way as non-retarded people. 