The authors examined the relationship of three dimensions of behavioral change (Apathy, Depression, and Irritability) measured by the Problem Behaviors Assessment for Huntington's Disease (PBA-HD) to cognitive and motor indices of disease severity. The Apathy subscale was highly correlated with both cognitive and motor impairment; the Irritability and Depression subscales were not. The findings suggest that certain behavioral alterations are intrinsic to the evolution and progression of HD, whereas others are more variable and are independent of other indices of disease progression.