The use of MDMA/Ecstasy has increased among young people in many industrialised nations around the world since the mid-1990s. Although there is a lack of scientific consensus concerning the long-term consequences of Ecstasy use, reducing potential morbidity and mortality is an important public health concern. This article describes how young people characterise perceived long-term consequences associated with Ecstasy using three data sources: (1) qualitative interviews with 29 participants; (2) pile sort results from 20 participants who classified 15 psychoactive substances on the basis of perceived similarities; and (3) quantitative data on subjective memory impairment from 402 participants in our natural history study. Contrary to expectations, Ecstasy was classified midway between drugs perceived to be the most and least risky. Risks associated with Ecstasy use included two popular myths implying forms of brain damage—“draining spinal fluid” and “creating holes in brains”. Qualitative results also indicated that some young people are concerned about the potential effects of the drug on memory and as a cause of depression. About 20% (82) of the participants (n = 402) “agreed” or “strongly agreed” that Ecstasy has impaired their memories. Concern about these adverse consequences may provide opportunities for reducing potential harm associated with Ecstasy use.