Publisher Summary This chapter discusses that surgical treatment of brainstem lesions is limited by dense concentration of functionally important neural pathways, nuclei, and fibers in ponsvariolii and medulla oblongata, and the lack of reliable visible anatomical landmarks. Since most brainstem lesions are approached via the IVth ventricle, the presence of functionally intact brain tissue between ependyma and lesion already posses a potential risk due to the surgical corridor itself. The chapter explores that in pontine lesions, facial and abducens nerve deficits, as well as conjugated gaze palsies can affect the quality of life. Deficits of lower cranial nerve nuclei are severe life-threatening complications following the surgery of medullary lesions. The chapter reviews that direct electrical stimulation during surgery has emerged as a reliable and safe technique for the identification of superficially located nuclei and fibers, in order to define the safe entry zones into pons and medulla.