Symptomatic middle fossa cysts have not previously been described as complications of temporal lobectomy that has been performed to control complex partial seizures. A patient is described who developed a middle fossa cyst causing mass effect, intracranial hypertension, and neurological deterioration > 2 years after temporal lobectomy for complex partial seizures. An enlarging cyst with cerebrospinal fluid imaging characteristics was detected on neuroimages 1 year before neurological deterioration. The patient was treated by the insertion of a cystoperitoneal shunt for cerebrospinal fluid diversion. The potential causes of an acquired arachnoid cyst and hydrocephalus are discussed.