Serum lipid (triglycerides and cholesterol) concentrations were studied in 49 patients with acute pancreatitis (AP). The aims of the study were to investigate the prevalence of hyperlipidemia (HL) in patients with AP according to etiology and to evaluate whether HL precedes or is a consequence of AP. Moreover, we analyzed the relationship between HL and the development of pancreatic necrosis. At admission, 23 patients (47%) had HL: 9 of 19 patients with alcoholic pancreatitis, 5 of 18 patients with biliary pancreatitis, and 9 of 12 patients with AP of miscellaneous etiologies (p less than 0.05). Severe HL (serum triglycerides greater than 20 mmol/L) was observed in five patients. Serum lipid levels in patients with AP and HL decreased markedly during the first 72 h of evolution, but remained slightly above the upper normal limit in most of them after 15 d. The prevalence of HL was similar in edematous and necrotizing pancreatitis. Necrotizing pancreatitis was significantly associated with the presence of hypertriglyceridemia in conjunction with hypercholesterolemia (p less than 0.05). The observations that a) hyperlipidemia is an early event in acute pancreatitis, (b) serum lipid values decrease during the acute phase of the disease, (c) hyperlipidemia has a different prevalence in different etiologies, and (d) high serum lipid levels are not always associated to pancreatic necrosis suggest that HL is a preexistent metabolic abnormality with respect to AP. On the other hand, HL may play a role in aggravating AP.