Authors evaluated the sensitivity and specificity of DSM-IV and ICD-10 criteria and the cutoff value of the Memorial Delirium Assessment Scale (MDAS) in diagnosing postoperative delirium in 260 cardiac surgery patients. Incidence of delirium diagnosed on the basis of DSM-IV and ICD-10 criteria, and with the use of the MDAS was 11.5%, 9.2%, and 6.5%, respectively. The DSM-IV criteria for delirium were found to be more inclusive than those of ICD-10. The cutoff point of 10 of the MDAS was optimal in relation to the presence or absence of delirium after cardiac surgery.