Dexmedetomidine is a potent alpha2 adrenergic agonist, with sedative and analgesic properties which may make it a suitable sedative agent for procedures on paediatric patients. A six-year-old boy required sedation for stereotactic radiosurgical ablation of an arteriovenous malformation on two occasions. Sedation with dexmedetomidine was planned, with increased dosage used on the second occasion. On both occasions dexmedetomidine was inadequate as a sole agent and required supplementation with other agents.