The British literature on spontaneous hyperinsulinism due to islet cell neoplasms is reviewed with reference to the psychiatric presentation of the disease. Two further cases of islet cell adenoma which were diagnosed in a psychiatric hospital are described. Of the total 39 patients, 7 were diagnosed in a psychiatric hospital, 1 of them at post mortem. Six further patients had been misdiagnosed as having hysteria or neurasthenia. This estimate of psychiatric presentation (33 per cent.) is probably too low. The importance of psychiatrists being familiar with the condition is emphasised. The differential diagnosis is discussed.