A new self-report measure of impulsivity was developed to provide group administration and economy of scoring. An initial set of 26 items was constructed to tap various aspects of impulsivity, or the tendency to respond quickly without thinking. The items were administered to 346 male undergraduate students, primarily freshmen and sophomores. Item analysis indicated that 18 of the items could be legitimately combined into a single scale. Reliability (coefficient alpha) was .68. Results of a cross-validation study of 363 similar subjects showed that the 18 items had stable trace lines and a coefficient alpha of .67. Mean scores, standard deviations, and standard error of measurement were also virtually identical for the two samples of respondents. It was concluded that the new Impulsivity Scale had sufficient psychometric properties and practical advantages to warrant its use in educational and research settings. Moderate, rather than high, reliability may have been due to the four-point response scale, or the fact that impulsivity is a multidimensional rather than a unidimenstional construct. (The 18-item Impulsivity Scale is appended.) (Author/GDC)