Radiosurgery is often used to treat arteriovenous malformations (AVMs) located in deep brain locations. Most of these procedures are successful not only in obliterating the AVM but also in decreasing the frequency and severity of associated seizures. Although radiosurgery is occasionally associated with the development of easy-to-control seizures immediately postoperatively, there have been no reports of intractable epilepsy developing after radiosurgery. In this report, however, a case is presented in which a patient underwent gamma knife surgery (GKS) for an AVM, after which intractable epilepsy and mesial temporal sclerosis (MTS) gradually developed. A 37-year-old right-handed woman underwent GKS for a right mesial parietotemporooccipital AVM. One year later, the AVM had reduced in size, but the patient began to experience complex partial seizures (CPSs). These CPSs initially occurred at a frequency of one per month, but 6 months later they were occurring every other week. She also started having secondarily generalized tonic-clonic seizures (GTCSs) once per month. Over the next year the frequency of her seizures gradually increased to several CPSs per day and two to three GTCSs per week, despite treatment with various combinations of antiepileptic drugs. By this time her AVM had decreased to one half of its original size. Video-electroencephalography monitoring demonstrated that both the CPSs and GTCSs were arising from the right posterior quadrant. Magnetic resonance imaging revealed not only the presence of the right-sided AVM, but also right-sided MTS. The patient underwent surgical resection of the AVM and right temporal lobectomy. She has been free from seizure for longer than 1 year. Radiosurgery may be associated with intractable epilepsy and MTS.