Objective To investigate the causes, characteristics, diagnosis and treatment of severe acute pancreatitis (SAP) complicated with mental disorders. Methods The clinical data of 86 patients with SAP complicated with mental disorders who had been admitted to Union Hospital of Tongji Medical College from 2000 to 2007 were retrospectively analyzed. The causes, clinical manifestations, treatment and prognosis were analyzed. Results Of the 86 patients, 38 were caused by internal milieu disorder, 9 by pancreatic encephalopathy, 23 by infectious-toxic encephalopathy, and 16 by Wernicke encephalopathy. The manifestation of the patients with SAP complicated with mental disorders was complex, varied and nonspecific. Individualized treatment was applied to all patients after the analysis of the causes, and most patients recovered except 14 who died of hemorrhage or multiple organ dysfunction syndrome. Conclusions Internal milieu disorder should be first considered when patients have mental disorders which occurred at the early phase of SAP, then pancreatic encephalopathy should be considered. The infectious-toxic encephalopathy and Wernicke encephalopathy should beware of when the mental disorders occur in the late phase of SAP. Individualized treatment according to the causation and comprehensive treatment are effective in preventing and treating mental disorders which occurred in the course of SAP. Key words: Severe acute pancreatitis; Mental disorders