In general, the invention is directed to techniques for implantation of a low-profile implantable medical device (IMD) in the body of a patient. In an exemplary embodiment, the low-profile IMD is implanted under the scalp. When the treatment or monitoring site is in or on the head of the patient, the low-profile IMD can be implanted under the scalp proximate to the treatment or monitoring site. In one embodiment, the invention is directed to a method that includes making an incision in the scalp of a head of a patient to create a scalp flap, exposing a skull beneath the scalp flap, creating a pocket between the scalp and the skull, and placing at least a portion of a low-profile IMD in the pocket. The low-profile IMD may include a plurality of modules, covered in part by a flexible overmold.