Five of six children with severe familial primary hypertriglyceridemia in the first three to five years of life had what we believe is a new clinical feature, intermittent swelling of the limbs and scrotum. This was associated with higher levels of plasma triglyceride (greater than 2,000 mg/dL) and, in some instances, venous stasis of the affected part. All children had severe elevation of plasma chylomicron levels and mild elevation of very low-density lipoprotein levels. Four of the subjects were siblings who demonstrated heterogeneity in plasma lipase activities after heparin sodium administration. The clinical features and the lipase heterogeneities suggest that these patients possibly have an unusual variant of primary hypertriglyceridemia.