Chylomicrons accumulating in plasma obtained after an overnight fast are always abnormal and can be detected in association with triglyceride levels above 1000 mg per dl. The chylomicronemia syndrome is associated with marked hypertriglyceridemia (plasma triglyceride level above 2000 mg per dl), abdominal pain or pancreatitis, eruptive xanthomata, lipemia retinalis, dyspnea, mental aberrations, and other minor findings. The marked hypertriglyceridemia is usually due to the interaction of a common familial form of hypertriglyceridemia and a common acquired form of hypertriglyceridemia secondary to another disease, drug, or alcohol. Rarely, genetic abnormalities in lipoprotein lipase are the cause of the marked hypertriglyceridemia. Therapy that successfully lowers plasma triglyceride levels is associated with clearing of the symptoms and signs of the chylomicronemia syndrome and prevention of its recurrence.