Background/Aims: Serum lipid concentrations react during acute disease. We sought to measure changes in the serum lipid profile during acute pancreatitis and ascertain whether these changes were associated with the severity of the disease. Methods: A total of 233 patients (71% male, median age 48 years) hospitalized for acute pancreatitis were included in the study. The most common etiology for acute pancreatitis was alcohol (n = 131, 56%), followed by biliary (n = 48, 21%) and idiopathic pancreatitis (n = 36, 16%). Serum lipid levels were measured enzymatically. We analyzed samples obtained during the first days of hospitalization and later follow-up samples to measure changes during the course of the disease. Results: We report profound changes in the serum lipid concentrations during acute pancreatitis. Serum total cholesterol, high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol concentrations measured within 2 days of admission (n = 203) were significantly lower in patients who developed severe pancreatitis (3.20 vs. 3.80 mmol/l, p = 0.001; 0.72 vs. 1.05 mmol/l, p < 0.000, and 1.60 vs. 2.14 mmol/l, p < 0.000, respectively). Low serum total cholesterol, HDL cholesterol and LDL cholesterol concentrations were moreover associated with in-hospital mortalities and longer hospitalization (p < 0.05). In the subgroup analysis, the findings remained statistically significant in patients with alcohol-induced acute pancreatitis. Conclusion: Levels of serum total cholesterol, HDL cholesterol and LDL cholesterol are significantly lower in patients with severe acute pancreatitis and are associated with longer hospitalization.