Lumbar subarachnoid-peritoneal shunts are used occasionally in the treatment of communicating hydrocephalus. A 5-year-old girl with meningomyelocele and communicating hydrocephalus developed unilateral ureteral obstruction secondary to extrinsic compression by a nonfunctioning shunt of this type. Progressive hydronephrosis was reversed by excision of the shunt and ureterolysis.