We report the development of aseptic meningitis in 3 patients with aneurysms treated with hydrogel-coated coils. Patients presented with febrile meningeal syndromes during the 24 hours following the procedures and responded to corticosteroids. One of them developed delayed hydrocephalus that required treatment with a ventriculoperitoneal shunt. Aseptic meningitis is one of the important complications related to hydrogel-coated coils that should be recognized. More information based on the posttreatment surveillance after use of hydrogel-coated coils is required.