SUMMARY Posterior hypothalamotomy is a relatively simple stereotactic procedure. The radiological determination of the target and its physiological corroboration by electrical stimulation are accurate. The lesions have always been made in the site of maximum sympathetic response. In this respect, the cardiovascular changes (hypertension and tachycardia), which are always elicited from a more restricted area, are of particular importance. Depth recordings, however, have been less useful. Undesirable side-effects, if present, were mild and transitory. There was no postoperative intelligence deficit, at least with the standard tests.Soon after the suggestion that particular areas of the brain were involved in emotional behaviour, Bard (1928) showed that removal of all nervous tissue rostral, dorsal, and lateral to the hypothalamus did not abolish sham rage phenomena in decorticate preparations. However, sections caudal to the hypothalamus eliminated this response (Bard and Rioch, 1937;Bard, 1939).Hess, in 1927, using chronically implanted electrodes in cats, elicited a wide variety of 'affective-defensive' reactions from hypothalamic stimulation, which were of somatic, autonomic, and behavioural type. These purposeful and well coordinated responses could be obtained from a relatively extensive area, although with lower threshold from the perifornical region (Hess, 1954(Hess, , 1969.Later papers suggest that a wide variety of behavioural patterns depend upon relatively specific hypothalamic structures (Ranson and