The syndrome of inadequate secretion of antidiuretic hormone (SIADH) following treatment with a tricyclic antidepressant is demonstrated using the example of a 70 year-old man admitted for weakness and cognitive disturbances. Because of incontinence he had been periodically treated since 1989 with imipramine (Tofranil) by his family doctor. On admission he was seriously hyponatriemic and had low plasmatic osmolality, significantly lower than urinary osmolality. Creatinine, urea and uric acid in serum were also below normal values. Like other drugs tricyclic antidepressants can rarely induce an increased release of ADH by direct hypothalamic stimuli. In this patient imipramine was terminated and within a few days of reduced fluid intake and substitution of sodium a sustained clinical improvement and normalisation of laboratory parameters was noted. The patient was discharged to his home after three weeks.