The clinical results of electrical stimulation in medial thalamic regions for cancer pain have been correlated with the exact location of the stimulation sites. Five brains were examined by post-mortem histology. Chronic implantation of enamel coated platinum-iridium electrodes for up to 17 months caused relatively mild glial and neuronal reactions and no significant haemorrhage or infarction. The anatomical verifications showed that the electrodes were close to, but not exactly in, the regions defined by the stereotactic coordinates. From the clinico-anatomical correlations it appears that good pain relief can be obtained by electrical stimulation in the periventricular gray region of the posterior thalamus.