Background: 1,4-Butanediol is an industrial solvent that, when ingested, is converted to γ-hydroxybutyrate, a drug of abuse with depressant effects, primarily on the central nervous system. After reports of toxic effects of γ-hydroxybutyrate and its resultant regulation by the federal government, 1,4-butanediol and γ-butyrolactone, another precursor of γ-hydroxybutyrate and an industrial solvent, began to be marketed as dietary supplements. We investigated reports of toxic effects due to the ingestion of 1,4-butanediol and reviewed the related health risks. Methods: From June 1999 through December 1999, we identified cases of toxic effects of 1,4-butanediol involving patients who presented to our emergency departments with a clinical syndrome suggesting toxic effects of γ-hydroxybutyrate and a history of ingesting 1,4-butanediol and patients identified through public health officials and family members. We used gas chromatography-mass spectrometry to measure 1,4-butanediol or its metabolite, γ-hydroxybutyrate, in urine, serum, or blood. Results: We identified nine episodes of toxic effects in eight patients who had ingested 1,4-butanediol recreationally, to enhance bodybuilding, or to treat depression or insomnia. One patient presented twice with toxic effects and had withdrawal symptoms after her second presentation. Clinical findings and adverse events included vomiting, urinary and fecal incontinence, agitation, combativeness, a labile level of consciousness, respiratory depression, and death. No additional intoxicants were identified in six patients, including the two who died. The doses of 1,4-butanediol ingested ranged from 5.4 to 20 g in the patients who died and ranged from 1 to 14 g in the nonfatal cases. In some cases there was evidence of addiction and withdrawal. Conclusions: The health risks of 1,4-butanediol are similar to those of its counterparts, γ-hydroxybutyrate and γ-butyrolactone. These include acute toxic effects, which may be fatal, and addiction and withdrawal.