BACKGROUND: Neuropsychiatric symptoms and behavioral changes, known as behavioral and psychological symptoms of dementia (BPSD), are often observed in patients with dementia. BPSD impairs a patient's quality of life, increases the burden on the caregivers, and can be a predictor of the need for institutionalization. BPSD can aggravate on holidays or at night, when general psychiatric clinics are closed. When psychiatric symptoms aggravate on holidays or at night in patients with psychiatric disorders other than dementia, such as schizophrenia and manic psychosis, the patients visit psychiatric emergency hospitals. However, it has not been assessed whether patients with dementia visit psychiatric emergency hospitals for the treatment of BPSD on holidays or at night, although dementia patients are increasing and account for 10.5% of psychiatric outpatients in Japan. AIMS: To determine the percentage of dementia patients with BPSD in all psychiatric patients who visit psychiatric emergency hospitals, and the characteristics of patients with BPSD in Japan. METHOD: We developed two questionnaires. One was for psychiatric emergency hospitals and assessed the numbers of all patients, patients over 65 years old, and patients over 65 years and with BPSD or BPSD-like symptoms, who visited the psychiatric emergency hospitals on holidays or at night. The other questionnaire was for each patient over 65 years and with BPSD, and assessed the patients' characteristics, including their diagnosis, sex, what kinds of BPSD or BPSD-like symptoms brought them to the hospital, and whether they had visited a psychiatric clinic or hospital during the preceding 12 months. The questionnaires were sent to 360 hospitals that belong to the Japan Psychiatric Hospitals Association and treat patients with acute psychotic symptoms or dementia. This prospective survey was conducted from October 1 to November 30, 2009. RESULTS: One hundred and forty-three hospitals returned the questionnaires (response rate: 39.7%). In the survey period, 3,527 patients visited the psychiatric emergency hospitals on holidays or at night, but only 67 patients over 65 years old (1.9%) visited the hospitals for BPSD or BPSD-like symptoms. Thirty-four of the 67 patients were men, and their average age was 79.4 +/- 6.4 years old. Thirty-five patients had visited but 25 patients had never visited psychiatric clinics or hospitals during the preceding 12 months. Eight patients had physical complications that required examination for several days, while 57 patients did not require such treatment. Forty-seven patients were diagnosed with dementia. Patients with Alzheimer's disease (AD) (29 patients) were the most common, followed by those with vascular dementia (VaD) (8 patients) and those with dementia with Lewy bodies (DLB) (4 patients). Among the 47 patients with dementia, agitation/aggression was the most frequent BPSD symptom (30 patients), followed by irritability (18 patients) and aberrant motor behaviors (17 patients). The BPSD symptoms observed at the psychiatric emergency hospitals differed due to the causative dementia. Agitation/aggression, aberrant motor behaviors, and irritability were the most frequent causative symptoms in AD, agitation/aggression and irritability were the most frequent causative symptoms in VaD, and hallucinations and illusions were the most frequent causative symptoms in DLB. CONCLUSIONS: Our survey revealed that few patients over 65 years old visited psychiatric emergency hospitals for BPSD on holidays or at night in Japan, and that many of them had not regularly visit psychiatric clinics or dementia hospitals in the preceding 12 months. These results indicate that dementia patients need to visit their doctors regularly to avoid visiting psychiatric emergency hospitals on holidays or at night, and caregivers should be aware that they can visit psychiatric emergency hospitals for the treatment of BPSD on holidays or at night.