The value of the Acute Physiology and Chronic Health Enquiry (APACHE-II) score, the Simplified Acute Physiology score, and the Medical Research Council (MRC) sepsis score were compared with clinical assessment and Ranson and Imrie scores in the evaluation and monitoring of acute pancreatitis in 290 attacks. Attacks were graded mild (231) if uncomplicated, or severe (59) when major organ failure or a pancreatic collection occurred. Only APACHE-II scores were available at the time of admission; they correctly predicted outcome in 77% of attacks and identified 63% of severe attacks, compared with 44% achieved by clinical assessment. After 48 h, APACHE-II was most accurate, and correctly predicted outcome in 88% of attacks, compared with 69% for Ranson and 84% for Imrie scores. APACHE-II predicted 73% of pancreatic collections at 48 h, compared with 65% for Ranson and 58% for Imrie scores. In acute pancreatitis, APACHE-II may facilitate rapid selection of patients for intensive therapy or clinical trials, improve comparison between groups of patients, and indicate that a pancreatic collection is probable.