BACKGROUND Long hospitalization is often needed to treat severe behavioral and psychological symptoms of dementia (BPSD), which places heavy demands on hospital resources. Consequently, patients with severe BPSD usually wait for a long time to be admitted. There is a need to identify factors related to long hospitalization to better manage resources of a psychiatric hospital. METHODS We surveyed 150 consecutive patients hospitalized in the neuropsychiatric units of three hospitals for treatment of BPSD from 11 May 2009 to 30 November 2010. Only patients with reliable relatives were included in the study. We evaluated data of the patients (demographics, cognitive impairment, activities of daily living, causal disease for dementia, dementia severity, and the amount of pension), their primary caregivers (demographics and care burden), and their doctors' years of experience in treating dementia. We followed up to 180 days and assessed the effect of these factors on the length of stay. RESULTS Of the 150 patients, 104 were discharged within 180 days and 46 were hospitalized for more than 180 days. Average length of stay for patients was 110.4 ± 58.1 days. In both univariate and multivariate Cox proportional hazard analyses, length of stay was longer for patients with smaller pensions and patients whose doctors had fewer years of experience in treating dementia. Length of stay was not found to be associated with any of the other variables. CONCLUSIONS Patients with smaller pensions and whose doctors had less experience in treating dementia tended to require longer hospitalization.