The Counterproductive Behavior Index (CBI) is a 120-item, true-false questionnaire developed to assess five aspects of counterproductive workplace behavior: Dependability Concerns, Aggression, Substance Abuse, Honesty Concerns, and Computer Abuse, plus an overall measure of Total Concerns. It also yields a Good Impression score. To assess predictive validity, undergraduates with significant work experience simulated persons who had each of the five counterproductive behaviors but were exercising care not to get caught trying to conceal that behavior. All differences between simulated and normative responding were highly significant, with a median sensitivity of.89 for a specificity of.90. For similar participants, construct validity correlations ranged from.37 though.72 with a median of.50, and the correlation of CBI Total Concerns with a Total Validity Index was.66. Test-retest reliabilities of the CBI scales ranged from.79 to.94 with a median correlation of.87. These compare favorably with previously reported internal consistencies (Cronbach alphas). Analysis of the CBI scores of the original normative group at different levels of Good Impression showed that none of the six Concerns scores were affected by attempts to make a good impression until the Good Impression score reached the 90th percentile.