This study examines the reliability and validity of the “Brief Irrational Thoughts Inventory” (BITI) in a sample of 256 justice-involved youths. The BITI is a questionnaire used to determine the nature and severity of irrational thoughts related to aggressive (externalizing), sub-assertive (internalizing), and distrust-related behavior in adolescents with conduct problems. The results of this study demonstrated adequate internal consistency reliability and supported validity of the BITI in terms of construct, convergent, concurrent and divergent validity. Construct validity was assessed using a confirmatory factor analysis. The BITI proved to be measurement invariant for sex and ethnic origin, i.e., the results indicated that items were interpreted in a similar way by boys and girls as well as native and non-native Dutch respondents. The BITI also proved to be insensitive to intelligence, education, and age (divergent validity). However, weak to moderate correlations were found between the degree of social desirability and irrational thoughts related to aggressive (externalizing) and distrust-related behavior (BITI). Finally, concurrent validity was satisfactory, with the exception of thoughts related to sub-assertive (internalizing) behavior.