The Barratt Impulsivity Scale (BIS), a 30-item self-report measure, is one of the most commonly used scales for the assessment of the personality construct of impulsiveness. It has recently marked 50 years of use in research and clinical settings. The current BIS-11 is held to measure 3 theoretical subtraits, namely, attentional, motor, and non-planning impulsiveness. We evaluated the factor structure of the BIS using full information item bifactor analysis for Likert-type items. We found no evidence supporting the 3-factor model. In fact, half of the items do not share any relation with other items and do not form any factor. In light of this, we introduce a unidimensional Barratt Impulsiveness Scale-Brief (BIS-Brief) that includes 8 of the original BIS-11 items. Next, we present evidence of construct validity comparing scores obtained with the BIS-Brief against the original BIS total scores using data from (a) a community sample of borderline personality patients and normal controls, (b) a forensic sample, and (c) an inpatient sample of young adults and adolescents. We demonstrated similar indices of construct validity that is observed for the BIS-11 total score with the BIS-Brief score. Use of the BIS-Brief in clinical assessment settings and large epidemiological studies of psychiatric disorders will reduce the burden on respondents without loss of information. (Contains 6 tables and 1 figure.)