A caution is advised for the use of electroconvulsive therapy (ECT) in patients with space-occupying intracranial lesions. The use of ECT in the presence of arachnoid cyst has been reported only in 10 cases in the literature. Here, we report a case of severe depression with psychotic symptoms who was found to have an arachnoid cyst of 3.4 × 1.6 cm in the left temporal region. The patient received a course of 12 ECT treatments without any complications and had significant improvement in symptoms. Magnetic resonance imaging after completion of ECT did not reveal any change in size of the arachnoid cyst.