ObjectiveTo explore the characteristics of the criminal cases assessed by forensic psychiatry expertise in order to provide evidence for guiding forensic psychiatric practice, preventing and reducing criminal acts of patients with mental disorders. MethodsWe collected information of 3 720 criminal cases assessed in Forensic Psychiatry Department of Sichuan University, China from January 1997 to December 2011 by using the self-made questionnaire, and analyzed the demographic data, criminological characteristics and expert consensus of psychiatric diagnosis and legal ability. ResultsOut of 3 720 criminal cases, 3 211 (86.3%) were male, and 3 022 (81.2%) were between 18 and 45 years old. A total of 1 683 (45.3%) were married or remarried. A total of 3 178 (85.4%) were under junior middle school, and 3 221 (86.6%) were farmer or unemployed. Schizophrenia (46.7%), without psychosis (13.8%), mental retardation (9.6%) were the top three kinds of diagnosis. Homicide (42.7%), intentional injury (21.5%) and rape/indecency (8.1%) were the main crimes. A total of 1 616 (43.4%) were irresponsible, and 1 172 (31.5%) were with full responsibility. There was a significant correlation between the number of criminal cases in every year and years (rS=0.94,P=0.00), and significant correlation was also found between the percentage of mental disorder caused by drugs and years(rS=0.84,P=0.00), as well as the percentage of mental retardation and years(rS=0.72,P=0.00). ConclusionThe number of cases shows an increasing trend in forensic psychiatry assessment over years. Most of the suspects of criminal responsibility are young and middle-aged male with low level of education, farmer or unemployed. The top three diagnoses are schizophrenia, without psychosis and mental retardation.