A 68-year-old woman presented with severe headache 9 days after undergoing successful clipping of a right middle cerebral artery aneurysm. Postoperative imaging revealed increased perfusion and diffuse edema in the right frontotemporal cortex. A 57-year-old woman exhibited perseveration soon after undergoing successful clipping of an anterior communicating artery aneurysm. Postoperative imaging studies revealed increased perfusion and diffuse edema in the left frontal and insular cortex. The symptoms and diffuse edema gradually resolved in both patients. These two cases of hyperperfusion syndrome occurred in a series of 190 patients treated by clipping of unruptured cerebral aneurysms. Hyperperfusion syndrome is a rare complication following aneurysm surgery, especially surgery for unruptured cerebral aneurysms without temporary clipping.