Disruptive behavior associated with dementia is a major clinical problem, but there has been limited methodology for assessing it. This study describes the development of a set of rating scales used to measure four dimensions of disruptive behavior that present frequent problems in patients with dementia: physical aggression, verbal aggression, agitation, and wandering. In addition, a total disruptive behavior scale is derived by averaging scores from these four scales. A sample of 16 patients in a skilled nursing facility was used to test interrater reliability and validity of this instrument. Interrater reliability was quite favorable for all scales. There was clear evidence for convergent validity of all scales except the verbal aggression scale, where a substantial correlation was found with one relevant external measure but not the other. There was also favorable evidence of discriminant validity for all scales except the verbal aggression scale. Psychometric properties of this instrument appear to be promising and indicate that it has potential utility for further research on causes and treatments for disruptive behavior in demented patients.