Impulsivity is a trait that has received much attention in humans, but in dogs impulsivity is illdefined, and previous studies have tended to focus on aggression, rather than its more pervasive effect on behavior. The objective of this study was to develop a valid psychometric assessment tool of impulsivity in dogs. An owner report questionnaire was constructed using items generated by a survey of experts. Five hundred and seventy one dog owners returned the questionnaire and data were subjected to principal components analysis, revealing a three-factor structure: Factor 1: Behavioral Regulation, Factor 2: Aggression & Response to Novelty, and Factor 3: Responsiveness. The resulting Dog Impulsivity Assessment Scale comprised of 18 items demonstrated evidence of reliability and validity.