An implantable stimulator includes a device for delivering a stimulus and a casing having a first, metal portion and a second, portion which is formed from a plastic or polymer. A method of forming an implantable stimulator includes preparing a coil on a ferrite tube and molding a casing body on the coil, such that the coil is embedded in a wall of the casing which is formed of a plastic or polymer. Another method of forming an implantable stimulator includes forming an annular metal connector and molding a plastic or polymer casing body on the metal connector.