Two studies were conducted to demonstrate that maladaptive aspects of high and low Openness to Experience were related to characterological impairment and that this aspect of personality may define a new domain of personality dysfunction. The 55-item Experiential Permeability Inventory (EPI; containing 4 scales) was developed and demonstrated to have acceptable psychometric properties. Evidence of convergent, discriminant, and incremental validity was provided. These studies provide a methodological framework for identifying and developing aspects of personality dysfunction that can expand the comprehensiveness of the current set of Axis II disorders. Theoretical implications of the EPI are discussed.