The use of ecstasy (MDMA), one of the most popular substances among young people in the context of many leisure and fun activities, is moving from party and recreation circuits to high schools and college dorms, in many cases in combination with alcohol consumption. Bearing in mind the concurrent use of the two drugs and the "gateway" thesis of a progression from legal drugs to illegal ones, a causal(1) model of linkages among sensation seeking, attitudes toward alcohol and ecstasy consumption, and frequency of use was tested using structural equation modeling (SEM). The data were obtained from a sample of 450 high school students ranging in age from 14 to 18 (47% male, 53% female). An additional moderator analysis was performed in order to examine a possible moderating role of sensation seeking in the relationship between attitudes toward consumption and frequency of use of both alcohol and ecstasy. Results were consistent with the hypothesis that positive attitudes toward consumption mediate the effects of sensation seeking on drug use. In addition, whereas our results were coherent with the existence of direct effects of sensation seeking on drug use, these were only found in the case of alcohol consumption. However, a moderating effect of this same variable was observed in the relationship between positive attitudes toward ecstasy consumption and its frequency of use. General and specific clinical implications and limitations of these findings are discussed and future lines of research suggested. .