The nature of Type V hyperlipoproteinemia including mode of presentation, prominent clinical and biochemical features, and genetics, was examined in 29 adults presenting with the Type V lipoprotein phenotype. Initially 23 of the 29 patients had various metabolic stimuli (diabetes out of control, estrogenic agents, pancreatitis, ethanolism) superposed on their acute hypertriglyceridemia. After metabolic stabilization, 17 of the 29 subjects were shown to have familial hypertriglyceridemia. In the 17 kindreds with familial hypertriglyceridemia, the lack of a specific, distinctive genetic marker for the Type V genotype and for the Type IV genotype restricts the conclusion that the pattern of inheritance was consistent with an autosomal dominant trait.