The invention relates to a membrane implant (1) for treatment of cerebral artery aneurysms (10), wherein the implant can be implanted endovascularly into vessel segments (2) at the craniocerebral base of pathological (aneurysmatic) dilation (10) and, in combination with a stent, bridges the diseased vessel segment (2) from inside and disconnects it from the blood stream, wherein the membrane implant (1) comprises a biocompatible plastic membrane in the shape of a cylinder or a segment of a cylinder.