The popular dance drug ecstasy (3,4-methylenedioxymethamphetamine, or MDMA, and some analogues) causes selective and persistent neurotoxic damage of the central serotonergic system in laboratory animals. Serotonin plays a role in numerous functional systems in the CNS. Consequently, various abnormalities including psychiatric, vegetative, neuroendocrine, and cognitive disorders might be expected in humans following damage of the central serotonergic system. In recent years, the questions of possible functional disorders following ecstasy-induced neurotoxicity were addressed in several cross-sectional studies with drug users. In this review we summarize and evaluate the quality of design of these studies. Despite large methodological problems, evidence accumulates in favor of persisting brain damage in ecstasy users resulting in subtle cognitive deterioration. Findings of relatively low memory performance associated with heavy ecstasy use are highly consistent across different studies and user populations. In addition, low performance in tests of higher executive function were reported in some but not all studies. The important questions about progression, persistence, or reversibility of damage after long periods of abstinence have to be addressed in future studies with longitudinal design.