A composite lead body includes a rigid polymer material, such as silicone-polyurethane co-polymers, in a proximal portion of the lead body and a flexible polymer material, such as silicone, in a distal portion of the lead body. The flexible polymer material is molded in-situ about the end of the rigid polymer material, which is pre-formed, forming a junction at which the two polymers are bonded together, preferably in an interdigitated manner. The end of the rigid polymer is treated with a primer in order to facilitate the formation of a strong bond between the polymers. The molding process, advantageously, provides substantial control over the final shape of the molded polymer, inhibiting the formation of discontinuities in the shape of the lead body.