Abstract The purpose of the present study was to investigate the prevalence, distribution of psychiatric diagnoses, and treatment responses of patients with post-partum mental illness at an emergency unit at Chang Gung Memorial Hospital at Kaohsiung in Taiwan. During a 1 year period a total of 636 Taiwanese women received psychiatric consultation on their visits to the emergency room. Fifteen of these were noted to have post-partum mental illnesses. All subjects were followed up for a minimum of 3–6 months. The prevalence of patients with post-partum mental illness at an emergency unit at Chang Gung Memorial Hospital at Kaohsiung was 2.4% (15/636). The distribution of psychiatric diagnoses according to Diagnostic and Statistical Manual of Mental Disorders (4th edn; DSM-IV) criteria included eight cases of major depressive disorders (53.3%), three cases of bipolar I disorder (20%), three cases of schizophrenia (20%), and one case of psychotic disorder due to a general medical condition (6.7%). Four subjects manifested catatonic features. Of these four, three had complete remission in catatonic symptoms after receiving intramuscular injection of lorazepam. The fourth subject died of multiple medical diseases. The treatment results suggest that most of the clinical presentations in patients with post-partum mental illness could be relieved by antipsychotics, mood stabilizers or antidepressants. In addition, it was found that intramuscular injection of lorazepam was also effective in patients with catatonic features and post-partum depression or psychosis.