Abstract: A device (30) for treating aneurysms comprises a bag (31) removably attached to the distal end of a catheter (14), the bag being arranged to be inserted in an aneurysm (20) and being of flexible and stretchable material and being permeable to blood components. Once the bag is inserted, individual GD coils (18) are introduced therein. The bag is inserted by a shoulder (42) or a widened portion (50) of a guide wire (40) engaging a marker ring (46). The bag material may encourage clotting. In another embodiment the bag (131) is located around the end of the catheter (114) during insertion. When insertion is completed, electrolysable struts (32, 172) are removed to separate the bag from the catheter.