Shifts in the conceptualization of psychopathology have favored a dimensional approach, with the five-factor model (FFM) playing a prominent role in this research. However, reservations about the utility of the FFM in differentiating disorders have risen. In the current investigation, a "bottom-up" analytical method was used to ascertain the hierarchical structure of personality, with investigation of the specificity of the traits in categorizing diagnostic categories across an expanded array of psychiatric disorders. Following earlier investigations, which used a hierarchical structural approach, this study presents new results relating to the differentiation of several forms of psychopathology not included in these earlier analyses--bipolar disorder, psychotic disorders, problem gambling, posttraumatic stress disorder, and somatoform disorders--across distinct levels of a personality hierarchy based on the FFM. These results bolster the argument for the use of FFM personality traits in characterizing and differentiating psychiatric diagnostic groups.