['Globally, millions of subjects regularly use ecstasy, a drug popular due to its empathogenic and entactogenic effects. Dilutional hyponatraemia, mainly caused by direct stimulation of antidiuretic hormone (ADH) secretion by ecstasy, is among the many side effects of the drug (active substance 3, 4-methylenedioxymethamphetamine, MDMA). Severe, symptomatic hyponatraemia related to the use of MDMA has been reported in more than 30 cases. The mortality of this complication is high and mainly females are involved. Dramatic cases that reach the literature probably represent the tip of the iceberg. We decided to study the incidence of hyponatraemia in subjects using MDMA at an indoor rave party.', "The study was performed at the indoor event 'Awakenings', held in Amsterdam in the fall of 2010. The plasma sodium concentration was measured at the party using a point of care method in 63 subjects using MDMA and 44 controls. The use of MDMA was confirmed by a urine test.", 'The plasma sodium concentration in subjects using MDMA was significantly lower than in those not using the drug (138 ± 2 mmol/L versus 140 ± 2 mmol/L, respectively, P < 0.001). The overall incidence of hyponatraemia, defined as a plasma sodium concentration <136 mmol/L, was 14.3% in MDMA users (9/63 subjects). Most cases of hyponatraemia occurred in females, in whom the incidence was 26.7% (8 of 30 females), with lowest values of 133 mmol/L. The number of ecstasy pills ingested by the females developing hyponatraemia was not different from that ingested by those who did not develop this complication. Fluid intake in ecstasy users exceeded that of non-users, suggesting a dipsogenic effect of the drug.'] Do high incidence of mild hyponatraemia in females using ecstasy at a rave party?