Individuals with DSM-IV Cluster B personality disorders are at particular risk of violence toward self or others. Emotional dysregulation is likely to be a factor in such incidents and is a central issue addressed in therapies with personality-disordered individuals. This article reports findings from a study that developed an original 18-item measure of emotional dysregulation and administered the scale to 100 participants diagnosed with Cluster B personality disorders or traits. A 13-item scale (the General Emotional Dysregulation Measure or GEDM) reflecting general emotional arousal and dysregulation of negative affect was derived using principal components analysis. The GEDM demonstrates good reliability and validity and correlates significantly with other established measures of affect. This measure is seen as potentially useful in clinical social work practice and in future investigations of the relationships among emotional dysregulation, personality disorders, substance abuse, and violence. (Contains 3 tables.)