Are the behavioral disturbances of dementia a primary manifestation of a devastating degenerative brain disease or a consequence of a demented patient's inability to cope with a hostile environment that does not adapt to his or her needs? Our current state of knowledge regarding the origin of noncognitive symptoms in dementia does not allow us to neatly dichotomize behavioral disturbances into either syndromes that can be attributed to altered neurobiologic substrates or behavioral reactions to a change in social routine or environment. The best fit model is one that incorporates biologic (neurochemical, neuropathologic, or genetic); psychological (premorbid personality and behavior, and response to stress); and social (environmental change and caregiver factors) aspects. For any particular symptom or group of symptoms, the relative input from each causal source can vary and may change in the future as our knowledge and understanding grow. The importance of an interactive causal model is that is has direct and immediate relevance to the development of treatment strategies.