Knowing how commonly used drugs affect performance monitoring is of great importance, because drug use is often associated with compromised behavioral control. Two of the most commonly used recreational drugs in the western world, 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") and ethanol (alcohol), are also often used in combination. The error-related negativity (ERN), correct-related negativity (CRN), and N2 are electrophysiological indices of performance monitoring.The present study aimed to investigate how ethanol, MDMA, and their co-administration affect performance monitoring as indexed by the electrophysiological correlates.Behavioral and EEG data were obtained from 14 healthy volunteers during execution of a speeded choice-reaction-time task after administration of ethanol, MDMA, and combined ethanol and MDMA, in a double-blind, placebo-controlled, randomized crossover design.Ethanol significantly reduced ERN amplitudes, while administration of MDMA did not affect the ERN. Co-administration of MDMA and ethanol did not further impair nor ameliorate the effect of ethanol alone. No drug effects on CRN nor N2 were observed.A decreased ERN following ethanol administration is in line with previous work and offers further support for the impairing effects of alcohol intoxication on performance monitoring. This impairment may underlie maladaptive behavior in people who are under influence. Moreover, these data demonstrate for the first time that MDMA does not affect performance monitoring nor does it interact with ethanol in this process. These findings corroborate the notion that MDMA leaves central executive functions relatively unaffected.