The reliability and validity of the self-report questionnaire How I Think (HIT), designed to assess self-serving cognitive distortions related to antisocial behavior, was tested among Swedish offender and nonoffender adults and adolescents (N = 364). The results showed self-serving distortions to be more common among offenders and to predict self-reported antisocial behavior when tested among adults. Confirmatory factor analysis revealed, in contrast to earlier findings, that the underlying structure of the HIT was best explained by a three-factor solution with one major cognitive factor, referred to as "criminal mind." It was concluded that the HIT, after further examination of its structural and divergent validity, could be used as a measure of criminal thinking in adults as well as in adolescents. (Published Abstract)