In this study, the authors describe the development and subsequent validation of an attention-deficit/hyperactivity disorder (ADHD) scale for young adults. The authors constructed 2 parallel forms of the scale to assess items that relate directly to DSM-IV criteria. Each form comprised Inattention, Hyperactivity, and Impulsivity subscales. Confirmatory factor analyses were conducted to assess the dimensionality of the scale, and the hypothesized structure was confirmed. In addition, the measures obtained show that the scale possesses satisfactory reliability with regard to the level of internal consistency, and there was equivalence between the 2 parallel forms. Furthermore, the relevance of the scale's content and its relationship to other variables was adequate. In sum, sufficient evidence is provided regarding the validity of the measures obtained with the ADHD scale, thus illustrating that the scale could be a useful tool to assess the symptoms of ADHD in a sample of young adults from the United States.