The authors report the cases of three children in whom symptomatic syringomyelia occurred de novo following an operation to relieve retethering of a previously treated lipomyelomeningocele. No patient had a Chiari malformation. In two cases, magnetic resonance imaging performed before the first operation did not show a syrinx. At the time of surgery to relieve retethering, it was discovered that one of these patients had a minor degree of terminal hydromyelia and the other had a prominent central canal within the conus medullaris. The third patient was initially studied by means of myelography, which gave no indication of a syrinx, and one was not found at the time of the surgery to release the retethering. Neurological deficits appeared abruptly within several months of operation in two children, and insidiously after 12 to 18 months in the other symptomatic individual. In all three cases, the syrinx involved the distal spinal cord adjacent to the site of the lipoma. Treatment consisted of syringosubarachnoid shunting, which arrested the progression of deficits but only partially reversed them. The details of each case are presented and the possible mechanism of syrinx formation discussed. Early recognition and treatment of this unusual but important problem are emphasized.