Severe pancreatic exocrine insufficiency was demonstrated in a 41 year old man with familial type I hyperlipoproteinemia (fat-induced hyperlipemia). Plasma triglyceride concentration failed to increase significantly with increased dietary fat intake, and fecal fat excretion was markedly increased. Indices of intestinal function were normal. Pancreatic enzyme therapy resulted in reduced fat excretion and increased plasma triglyceride concentration. Secretin stimulation tests revealed impaired duodenal fluid volume, bicarbonate and pancreatic enzyme responses. Insulin-dependent diabetes mellitus had been diagnosed three years earlier. No attacks of acute pancreatitis had occurred in the preceding 20 years, and it is suggested that pancreatic damage may have resulted from repeated subclinical pancreatic insults due to elevated plasma lipid levels. This report is the first to indicate that pancreatic exocrine insufficiency may occur as a late complication of hyperlipemic disorders in the absence of recurrent acute pancreatitis. Steatorrhea may not be apparent because of therapeutic restriction of dietary fat, and the first manifestation of pancreatic exocrine disease may be an amelioration of fat-induced hyperlipemia.