Dementia associated with Parkinson's disease (PDD) is a common problem and one that is associated with significant morbidity and mortality. Over the past decade, increasing research efforts and funding have been directed toward an improved understanding of PDD. Despite these efforts, fundamental gaps remain in our knowledge. Consequently, therapeutic progress has been frustratingly slow and incomplete. To significantly affect PDD, novel "disease-modifying" agents, rather than more traditional neurotransmitter replacement approaches, likely will be required.