The prion diseases are rare neurodegenerative conditions that cause complex and highly variable neuropsychiatric syndromes, often with remarkably rapid progression. Prominent behavioral and psychiatric symptoms have been recognized since these diseases were first described. While research on such symptoms in common dementias has led to major changes in the way these symptoms are managed, evidence to guide the care of patients with prion disease is scarce. The authors review the published research and draw on more than 10 years' experience at the U.K. National Prion Clinic, including two large prospective clinical research studies in which more than 300 patients with prion disease have been followed up from diagnosis to death, with detailed observational data gathered on symptomatology and symptomatic treatments. The authors group behavioral and psychiatric symptoms into psychotic features, agitated features, and mood disorder and describe their natural history, showing that they spontaneously improve or resolve in many patients and are short-lived in many others because of rapid progression of global neurological disability. Diagnostic category, disease severity, age, gender, and genetic variation are or may be predictive factors. The authors review the observational data on pharmacological treatment of these symptoms in the U.K. clinical studies and make cautious recommendations for clinical practice. While nonpharmacological measures should be the first-line interventions for these symptoms, the authors conclude that there is a role for judicious use of pharmacological agents in some patients: antipsychotics for severe psychosis or agitation; benzodiazepines, particularly in the late stages of disease; and antidepressants for mood disorder.