The purpose was 1) to prospectively determine the prevalence of adverse events necessitating intensive care unit (ICU) monitoring in gallstone pancreatitis (GP) and 2) To identify admission prognostic indicators that predict the need for ICU unit monitoring. Prospective laboratory data, physiologic parameters, and APACHE II scores were gathered on 102 patients with GP over 14 months. Adverse events were defined as cardiac, respiratory, or renal failure, gastrointestinal bleeding, stroke, sepsis, and necrotizing pancreatitis. Patients were divided into Group 1 (no adverse events, n=95) and Group 2 (adverse events, n=7). There were no deaths and 7 (7%) adverse events, including necrotizing pancreatitis (3), cholangitis (2), and cardiac (2). APACHE 11 > or = 5 (P < 0.005), blood urea nitrogen (BUN) > or = 12 mmol/L (P < 0.005), white blood cell count (WBC) > or = 14.5 x 10(9)/L, (P < 0.001), heart rate > or = 100 bpm (P < 0.001), and glucose > or = 150 mg/dL (P < 0.005) were each independent predictors of adverse events. The sensitivity and specificity of these criteria for predicting severe complications requiring ICU care varied from 71 to 86 per cent and 78 to 87 per cent, respectively. The prevalence of adverse events necessitating ICU care in GP patients is low. Glucose, BUN, WBC, heart rate, and APACHE II scores are independent predictors of adverse events necessitating ICU care. Single criteria predicting the need for ICU care on admission are readily available on admission.