The verification of the anatomical lesion sites in the brains of 11 patients who succumbed to their cancer after having stereotactic thalamotomies for the relief of chronic severe pain has given us a unique opportunity to correlate pain relief, sensory loss, and intrathalamic stimulation responses with the position and extent of the lesion produced in the thalamus. The anatomical techniques employed here were uniform in nine of the brains in this series. The whole brain serial section study of formalin-fixed brains has been described previously.6,14The brains were removed, fixed in 10% formalin, usually suspended by a ligature passed underneath the basilar artery. After four months, during which time the weight and volume of the brain were carefully measured, the brain was embedded in colloidan and cut at 35μ using the whole brain serial section technique and giant microtome. Every twentieth section was stained with a Loyez stain for