Ecstasy (MDMA; 3,4-methylenedioxymethamphetamine) has a well-recognized neurotoxic effect on central serotonergic (5-HT) systems in animals, and there is some evidence of persistent serotonergic dysregulation in human ecstasy users. Serotonin is believed to mediate impulsive behavior and effective decision-making. Thus, the aim of the present study was to investigate impulsive behavior and decision-making in abstinent regular ecstasy users. Three groups were compared: 'ecstasy users' (recreational ecstasy users who reported modest use of illicit drugs other than cannabis), 'polydrug controls' (ecstasy naïve illicit drug users), and 'drug-naïve controls'. All participants completed personal details and general drug history questionnaires, the National Adult Reading Test, Matching Familiar Figures Test (MFF20), a risky decision-making task (RDMT), and the Card Arranging Reward Responsivity Objective Test (CARROT). The groups did not differ on the CARROT measure of responsiveness to financial incentive; however, the ecstasy group displayed significantly elevated MFF20 impulsivity, and showed reduced discrimination between magnitudes of prospective gains and losses when making risky decisions, compared to the 'polydrug' and 'drug-naïve' control groups. These findings may reflect a vulnerability of 5-HT systems in the orbital prefrontal cortex and interconnected corticolimbic circuitry to the cumulative neurotoxic effects of ecstasy and have clinical significance for regular ecstasy users. The combination of elevated impulsivity and impaired use of reinforcement cues in uncertain decision-making may comprise risk factors for continued drug abuse and everyday functioning.