OBJECTIVES: The misdiagnosis of delirium may result in a delay of correct diagnosis and appropriate treatment of the delirium. Additionally, aggravation of physical illnesses can occur. The objective of this study was to investigate patient characteristics in cases of misdiagnosed delirium upon psychiatric consultation in a university hospital. METHODS: Subjects included patients with delirium among all who we had consulted over a 12 week span. Psychiatric diagnosis was made by two well-trained psychiatrists by means of the DSM-IV-TR. Cognitive function, level of delirium, and physical function were evaluated by the Korean version of Mini Mental Status Examination (MMSE-K), the Delirium Rating Scale-Revised-98 (DRS-R-98), the Clinical Global Impression-Severity (CGI-S), the Eastern Cooperative Oncology Group Performance Status (ECOG-PS), and the Global Assessment of Functioning Scale (GAF). In addition, we collected socio-demographic information, date of admission and consultation, present causes of consultation, and speculated psychiatric diagnoses made by referring physicians. RESULTS: Among 45 subjects with delirium, only 28 patients (62%) were diagnosed with delirium by referring physicians at the time of consultation. The remaining 17 patients (38%) had been diagnosed with other illnesses. The group of misdiagnosed patients tended to have a longer duration of formal education than those that had been correctly diagnosed. CONCLUSION: Early diagnosis and intervention of delirium can minimize subsequent problems related to delayed diagnosis. Therefore, it is vital to identify the factors related to misdiagnoses by referring physicians. This study showed that a longer duration of formal education is a contributing factor for the misdiagnosis of delirium. Longer education may cover up the typical symptoms of delirium. This can keep referring physicians from making a correct diagnosis. This study was a pilot study investigating diagnostic accuracy of delirium by referring physicians. Additional, well-controlled studies are warranted.