Although the prevalence of co-use of cannabis and 3,4-methylenedioxymethamphetamine (MDMA) is very common among polydrug users in western societies, few studies have tested the consequences on behavior, cognition or neurobiology. This review examines 23 articles published between 2002 and 2010 with an explicit focus on the combination, or administration, of MDMA and cannabis or cannabinoid agents. The aim was to provide a short overview on the latest human research concerning cognitive effects of co-consumption of MDMA and cannabis, and a more elaborate picture of the state of knowledge about the interaction of cannabinoid agents and MDMA from animal studies. It was found that recent retrospective studies on cognitive functions in long-term drug abusers point to an additive negative effect on different types of memory, as well as a cannabis-independent decrease in learning and decision-making in MDMA users. Behavioral experiments in rodents and in vitro studies investigating the combined effect of MDMA and cannabinoid agents demonstrate modulator effects of acute co-administration on measures like body temperature, conditioned reinforcement, and presumed neurotoxicity. As neural mechanism underlying these changes, an interaction between the cannabinoid system, especially cannabinoid receptor 1, and the serotonergic and dopaminergic system in the prefrontal cortex, nucleus accumbens, and hippocampus is suggested. In conclusion, there are few and somewhat contradictory studies examining the effects of co-use of these drugs on cognitive measures like impulsivity, memory and executive functions or underlying neurobiological alterations, and a shortage of animal studies examining long-term effects of chronic co-administration.