Many patients with mental disorders visit emergency departments (EDs). However, the majority of these patients do not receive psychiatric assessment. In the present study, we investigated the detailed proportion of patients with mental disorders visiting an urban ED in the largest northern city in Japan. A retrospective chart review study was performed at a University Hospital from January 2012 to December 2015. The reasons for psychiatric consultations made by ED staff, and the primary psychiatric diagnoses were investigated. Among all living patients, 20% of them received consultations. The most common reason for consultation was suicide attempt followed by agitation or insomnia. Of all diagnoses, organic mental disorder was the most frequent and the mean age was significantly higher than the other diagnostic groups. Our study indicated that the frequency of psychiatric consultation was high. This indicates the high demand for mental health services at the ED. A thorough psychiatric assessment can provide adequate psychiatric services to acute patients; thereby possibly preventing suicide attempters from later actually dying by suicide.