The authors describe a rare case of 15-year old patient with ruptured giant fusiform partially thrombosed aneurysm of fenestrated middle cerebral artery (MCA). The patient underwent surgical treatment: clipping of proximal and distal necks of aneurysm and thrombectomy. Intraoperative signs of MCA fenestration are described in details. The observation is instructive if a surgeon discovers 'double-necked' aneurysm for selection of adequate tactics of aneurysm occlusion.