Implantable medical devices have modular lead bores that are constructed from individual lead bore modules. A given modular lead bore utilizes the number of individual lead bore modules necessary for the particular implantable medical device. Each lead bore module has a lead bore passageway and a feedthrough passageway. An electrical contact is present within the lead bore passageway of each lead bore module and the electrical contact is aligned to the lead bore passageway of a lead bore module. Hermetic feedthrough assemblies are also present within the lead bore passageway of each lead bore module. A feedthrough pin passes through a hermetic feedthrough assembly within a feedthrough passageway of each lead bore module. Each feedthrough pin is electrically coupled to a corresponding electrical contact and the medical device circuitry.