OBJECTIVE Because the great majority of published cases of treated growing cranial fractures (GCFs) involved infants and children, the natural evolution of untreated GCFs is not well known. The question of whether untreated GCFs may cause progressive neurological deficits is controversial. METHODS This retrospective study is of GCFs treated between 1989 and 1997. Nine patients (eight male patients and one female patient; median age, 20.5 yr) with GCFs who underwent surgical intervention during the late stage are presented. The dural and cranial defects were repaired, and additional decompressive surgical procedures (cyst fenestration, n = 6; cyst excision, n = 1; cyst excision with cystoperitoneal shunting, n = 2) were performed for all patients. This is the largest of the published series. RESULTS All of the patients had histories of severe head trauma that occurred during childhood. The average age at the time of the onset of symptoms was approximately 13.1 years, and the interval between head injury and first symptom ranged from 8 to 13 years. All of the patients had lytic lesions in the cranium. Headache was the most common symptom, and of eight patients, seven improved completely and one improved partially. One of four epileptic patients was seizure-free postoperatively. None of the paresis improved, except in one patient. CONCLUSIONS We conclude that untreated GCFs may cause delayed onset neurological manifestations in addition to cranial growth asymmetry. GCFs, discovered incidentally in adolescence or adulthood without any neurological deficits, should be operated on as soon as feasible to prevent further brain destruction. Cranioplasty with dural repair, in addition to cyst fenestration, should be considered as the essential procedure for the treatment of these lesions.