This paper examines a series of cases of confirmed hyponatremia collected from reports made to the London National Poisons Information Service from December 1993 to March 1996. 17 of 135 ecstasy-related cases concerned hyponatremia, and included 2/17 (11%) fatalities. (135 of 13,762 cases from this time period were reported as ecstasy-related, or 0.009% of cases overall). 41% of the hyponatremia cases were in men (7), and 59% (10) were in women; both fatalities were women. The presence of MDMA was confirmed in 59% (10/17) of the cases reported. Consuming excessive amounts of alcohol or non-alcoholic beverages was reported in 59% (10) cases. Full recovery was reported in 14 cases (1 reported aspiration pneumonia requiring tracheotomy). All patients developed symptoms of hyponatremia within 12 h of ecstasy ingestion, and while doses varied from 0.5 to 2 tablets, presentation of hyponatremia was fairly uniform, involving headache, vomiting, drowsiness or bizarre behavior, and seizures. 6 of 17 cases (35%) were diagnosed with syndrome of inappropriate secretion of anti-diuretic hormone (SIADH). The authors did not recommend diuretics in the treatment of ecstasy-related hyponatremia, except in the case of cerebral edema (swelling of the brain). The authors speculate that using hypertonic saline could treat or reduce the severity of hyponatremia in some cases. Though not discussed by the authors, this case series of ecstasy-related hyponatremia is notable for its failure to find a strong gender disparity in the occurrence of hyponatremia; 41% of the cases in this sample were men, as compared with approximately 15% men reported in a general review (Baggott et al. 2001, on-line). It is unclear why gender differences in hyponatremia were less prominent in this sample. Examination of this case series suggests that hyponatremia associated with ecstasy use has an identifiable presentation, and that symptoms of hyponatremia may develop after the acute effects of ecstasy have subsided.