Objective: To test whether the Adult Self-Report Scale for ADHD, six-items version (ASRS-6), measures inattentiveness and hyperactivity independently. Method: The ASRS-6 was completed by 234 university students and 157 outpatients treated for drug dependence. In both samples, the ASRS-6 was subjected to two confirmatory factor analyses, one testing a one-factor model and the other testing a model with two correlated factors indicating inattentiveness and hyperactivity, respectively. Test-retest reliability of the subscales was tested on a subset of the student sample ("n" = 25). Results: In both samples, the one-factor solution did not fit the data, but the two-factor solution fit the data better. Subscales differed in their correlates in ways that mirror the correlates of inattentiveness and hyperactivity in the published literature on ADHD. In the student sample, the test-retest reliability was adequate for hyperactivity ("r" = 0.70) and inattentiveness ("r" = 0.77). Conclusion: The ASRS-6 measures two correlated constructs, rather than one unitary construct. (Contains 3 tables.)