Ecstasy users have reported that dry mouth, jaw tension and tooth grinding were common side effects of its use although the influence of these effects upon toothwear have not been previously investigated. OBJECTIVE: This study aimed to compare incisal and occlusal toothwear in Ecstasy users and a group of non-users of Ecstasy but users of other drugs. METHODS: Groups were established by a snowball peer information network from visitors to the "drop-in" Maryland Centre in Liverpool. Volunteers completed a questionnaire about social life, drug use and diet. Clinical examination for wear on the incisal edges and on canine tips was conducted with a mirror and probe, whereas occlusal wear was recorded in impressions and subsequently scored from stone replica casts. The degree of toothwear was scored according to the criteria of the Tooth Wear Index (Smith & Knight, Br Dent J 1984;157:16). RESULTS: Ecstasy users (n = 30) were compared with non-users (n = 28). Toothwear through the enamel into the underlying dentine occurred in 18 (60%) Ecstasy users but in only three (11%) non-users. The overall mean toothwear score in Ecstasy users was 0.63 compared with 0.16 in non-users (t = 4.34, P < 0.001). Dry mouth was reported by 93% of Ecstasy users whilst 89% stated that they clenched or ground their teeth after taking the drug. Tooth grinding commonly continued into the following morning. Carbonated (acidic) beverages were consumed by 93% of the users with a mean of three cans per "trip". CONCLUSION: The severity of toothwear and the number of teeth affected were greater in Ecstasy users than in a group of non-users. The occlusal surfaces were more commonly affected than the incisal, which may indicate jaw clenching rather than grinding as a feature of Ecstasy-induced muscle hyperactivity.