An insulin-dependent 26-year-old woman was complaining of nocturnal attacks of transient right hemiplegia. Hypoglycemia was found to be present at the time of each attack, and further investigations showed that these neurological disorders were related to an overdose of insulin. The authors discuss the effects of hypoglycemia on the brain and the pathogenetic theory of "hypoglycemic hemiplegia", involving selective neuronal vulnerability, regional blood flow disturbances or underlying ischaemic disease.