OBJECTIVE: To describe the clinical features of gamma-hydroxybutyrate (GHB) and gamma-butyrolactone (GBL) toxicity. METHODS: Retrospective case-study of 65 GHB and GBL intoxications seen in an urban emergency department. RESULTS: 63% of intoxications occurred in male patients. The median age was 24 years (range 16-41 years). 65% co-ingested alcohol or illicit drugs, mostly MDMA and cocaine. 83% presented with coma. The mean+/-S.D. time to regain consciousness among comatose patients was 111+/-61 min and was significantly longer in patients who co-abused illicit drugs such as cocaine or MDMA (155+/-60 min). Bradycardia occurred in 38%, hypotension in 6% and hypothermia in 48%. Agitation was observed in 17% of all patients and was significantly more frequent in patients with alcohol co-use (29%). Vomiting occurred in 31% of all patients and tended to be more frequent in patients who co-used alcohol (39%). Management of GHB and GBL overdose was supportive. Four patients needed admission to an intensive care unit for mechanical ventilation (6%). CONCLUSIONS: Overdosing of GHB and GBL frequently results in non-reactive coma reflecting the severity of poisoning. Multiple drug use is common and significantly influences the clinical presentation.