A 35-yr-old man with moderate hypertriglyceridemia, associated with a positive family history for hyperlipidemia, developed chylomicronemia with abdominal pain, muscle pain, and splenomegaly while being treated with cimetidine for a duodenal ulcer. The chylomicronemia and the pain subsided after the drug was stopped. When the patient was rechallenged with the drug 6 mo later, the chylomicronemia reappeared after a treatment period of 6 days. Chylomicronemia and its complications should therefore be considered as a potential risk when cimetidine is prescribed to patients with known hyperlipidemia.