[en] We enrolled six patients suffering from refractory chronic cluster headache in a pilot trial of neurostimulation of the ipsilateral ventroposterior hypothalamus using the stereotactic coordinates published previously. After the varying durations needed to determine optimal stimulation parameters and a mean follow-up of 14.5 months, the clinical outcome is excellent in three patients (two are pain-free; one has fewer than three attacks per month), but unsatisfactory in one patient, who only has had transient remissions. Mean voltage is 3.28 V, diplopia being the major factor limiting its increase. When the stimulator was switched off in one pain-free patient, attacks resumed after 3 months until it was turned on again. In one patient the implantation procedure had to be interrupted because of a panic attack with autonomic disturbances. Another patient died from an intracerebral haemorrhage that developed along the lead tract several hours after surgery; there were no other vascular changes on post-mortem examination. After 1 month, the hypothalamic stimulation induced resistance against the attack-triggering agent nitroglycerin and tended to increase pain thresholds at extracephalic, but not at cephalic, sites. It had no detectable effect on neurohypophyseal hormones or melatonin excretion. We conclude that hypothalamic stimulation has remarkable efficacy in most, but not all, patients with treatment-resistant chronic cluster headache. Its efficacy is not due to a simple analgesic effect or to hormonal changes. Intracerebral haemorrhage cannot be neglected in the risk evaluation of the procedure. Whether it might be more prevalent than in deep-brain stimulation for movement disorders remains to be determined.