Cocaine is an indirect sympathomimetic agent that acts in the nervous system to block the presynaptic reuptake of serotonin and catecholamines (dopamine, norepinephrine and epinephrine) and to increase their bioavailability at the post-synaptic receptors. The association of cocaine and hyponatremia has not been reported in adults. We describe a case of acute severe hyponatremia that followed smoking cocaine. We propose that cocaine, via its effect on the neurotransmitters, stimulates antidiuretic hormone release and leads to a syndrome of inappropriate antidiuretic hormone secretion.