Four children, ages 12 to 15 years, with intracranial arachnoid cysts complicated by increased intracranial pressure are reported from Children’s Hospital of Philadelphia, PA. They presented with recent onset or increasing headaches, exacerbated by the supine position. Visual acuity was normal. Optic discs were swollen. Opening pressures at LP were 37 to 54 cm H20. All failed to respond to conservative medical therapies, but symptoms improved after a surgical shunting procedure. The arachnoid cyst was in the left middle temporal fossa and was complicated by a Chiari I malformation in 3 patients; one patient had hydrocephalus diagnosed at 18 months and a posterior fossa cyst. Three patients were previously treated with a cystoperitoneal shunt before age 2 and required shunt revision. 
COMMENT. Usually benign, arachnoid cysts are rarely complicated by increased intracranial pressure that may require a surgical shunt procedure. The association of a Chiari I malformation with an arachnoid cyst in 3 of these patients is noteworthy, but a possible relation to the headaches and increased intracranial pressure is undetermined. Other symptoms sometimes associated with arachnoid cyst include attention deficit hyperactivity disorder, not alluded to in this report.