There has been an exponential increase of interest in the dark side of human nature during the last decade. To better understand this dark side, the authors developed and validated a concise, 12-item measure of the Dark Triad: narcissism, psychopathy, Machiavellianism. In 4 studies involving 1,085 participants, they examined its structural reliability, convergent and discriminant validity (Studies 1, 2, and 4), and test-retest reliability (Study 3). Their measure retained the flexibility needed to measure these 3 independent-yet-related constructs while improving its efficiency by reducing its item count by 87% (from 91 to 12 items). The measure retained its core of disagreeableness, short-term mating, and aggressiveness. They call this measure the "Dirty Dozen", but it cleanly measures the Dark Triad. (Contains 1 figure and 9 tables.)