This report is an analysis of neurological and psychiatric manifestations observed in 27 patients suffering from verified adenoma of the islet cell apparatus of the pancreas. In addition relevant laboratory data, mainly those related to the glucose metabolism and in the last 11 patients also the EEG findings are discussed.The clinical data were arranged in four groups: (1) autonomic-visceral, (2)somatic-neurological, (3) "psychomotor" manifestations and (4) seizures and seizure fragments.These four groups of data are then discussed in terms of anatomic-physiological levels using concepts established by Himwich. Our findings differ in several important aspects from those found in therapeutic insulin shock. An attempt is made to understand the reasons for this divergence.Glucose tolerance curves in a majority of our cases are diabetic in pattern and often also in level. "Flat" curves are the exception in our experience.The EEG findings are those to be expected in patients whose cerebral metabolism is depressed. In addition suggestive "convulsive" patterns such as spike-and-wave bursts are found in most of our patients, even those who had no clinical convulsive seizures.