To evaluate the efficacy and safety of Yokukansan, a traditional Chinese herbal medicine, for treating behavioral and psychological symptoms of dementia (BPSD) in patients with Parkinson disease (PD; n=7) and those with PD with dementia (PDD; n=7).BPSD are often seen in patients with senile dementia and have serious deleterious effects on the lives of patients and caregivers. Recent studies indicate that the traditional Chinese herbal medicine Yokukansan may be safe and beneficial for the treatment of BPSD patients.We treated 7 PD and 7 PDD patients for 4weeks with Yokukansan and observed them without Yokukansan for 4weeks. Changes in behavioral and psychological symptoms were evaluated every 4weeks according to the Neuropsychiatric Inventory (NPI) scale.Significant improvements in behavioral and psychological symptoms, particularly in the incidence and duration of hallucinations, were observed in most PD and PDD patients after 4weeks of Yokukansan treatment. No significant changes were observed in the laboratory tests, cognitive function, activities of daily living, or parkinsonism.Our results suggest that Yokukansan improves BPSD in both PD and PDD patients without worsening their cognitive function, ability to perform activities of daily living, or parkinsonism.