We compared the multiple organ system failure (MOSF) score, the Acute Physiologic and Chronic Health Evaluation (APACHE) II, and Ranson and Imrie scores for their predictive value in evaluating severity of acute pancreatitis. Of the 259 patients, 73 (28%) had severe disease. Fifty-two (20%) patients had organ system failure (OSF) on admission, and 59% of patients with severe disease had OSF. Shortly after admission, only MOSF and APACHE II scores were available, and in patients with severe disease, these predictions were correct in 64% and 60%, respectively. Forty-eight hours later, the MOSF score was the most sensitive, and correctly predicted outcome in 67% of patients, compared with about 60% for other scores. Of four scoring systems, only MOSF and APACHE II scores allowed repetitive assessment to monitor the course of the disease. MOSF score is organ-specific and may be better than APACHE II in reflecting disease activity. Our results suggest that the MOSF score is valuable in early identification and close monitoring of high risk patients and in deciding on therapy in these patients.