Ketonaemia is well documented as a consequence of prolonged starvation, acute alcoholism, and uncontrolled diabetes mellitus. However, its occurrence in acute pancreatitis has not been described. In this report, three patients who manifested ketoacidosis at the time of presentation of acute pancreatitis are described. In none of these patients could ketoacidosis be attributed to any of the well known pathogenetic factors such as ethanol, diabetes mellitus or prolonged starvation. In one patient, both the serum ketone titres and increased anion gap persisted for several days during the recovery period, despite appropriate therapy (including restriction of oral intake or nasogastric suction, intravenous fluids, and analgesic administration), before declining in parallel with a decrease in serum lipase levels, and became undetectable following near normalisation of serum lipase. Therefore, we believe that pancreatic ketosis or ketoacidosis may be a distinct syndrome with ketogenesis being promoted and maintained by extremely high circulating pancreatic lipase concentrations.