Elderly people are more likely to be affected by hyponatremia related to the use of specific inhibitors of serotonin recaptation. Doctors who treat old patients should be aware of this adverse effect which can be serious but is reversible. The observation of a new case of SIADH induced by fluoxetine in a 65 years-old patient is the opportunity to point out the main aspects of this pathological entity which must be suspected in case with hyponatraemia, blood hypoosmolality and high urinary osmolarity.