The syndrome of inappropriate antidiuresis (SIAD) is the commonest cause of hyponatraemia in hospitalised patients, accounting for 43% of patients with a plasma sodium concentration of <130 mmol/l [1]. Although there are virtually no data on mortality in SIAD, mortality in all-cause hyponatraemia has been reported to be elevated in almost every paper on the subject [2][3][4]. Hyponatraemic patients are also vulnerable to morbidity related to falls [5], fractures [6] and osteoporosis [7]. In the absence of separate studies in SIAD, it is widely accepted that patients who have hyponatraemia due to SIAD are vulnerable to the same risk of the morbidities and mortality associated with all-cause hyponatraemia. This has prompted considerable interest in whether treatment of hyponatreamia can improve outcomes in SIAD.Unfortunately, there is little data in the literature upon which to construct evidence based guidelines for the management of hyponatraemia due to SIAD. In the absence of a solid evidence base, there are controversial differences between the US recommendations [8] and the European guidelines [9] on treatment of SIAD. The US recommendations acknowledge that second-line treatment of SIAD, after failure of water restriction can be vaptans, urea or frusemide with sodium chloride supplementation, whereas the European Guidelines specifically advise against vaptans. So where are the gaps in our knowledge in the literature? The mortality in SIAD separately from that due to all-cause hyponatraemia is not known. Mortality studies have assessed the effects of hyponatraemia on death rate, without separating out the relative mortality of SIAD from other causes of hyponatraemia. In addition, as very few studies have firmly ascertained the full diagnostic criteria for SIAD in their study cohorts [10], the accuracy of data from many SIAD studies is questionable.The situation is complicated by the lack of studies on the response of plasma sodium to established treatments for SIAD. There are no prospective randomised-controlled trials which have reported the effects of water restriction, and many second-line treatments, in SIAD. There is however firm data on the response of SIAD-related hyponatraemia to treatment with vaptans; the randomised, placebocontrolled SALT studies showed that a mixed population of patients with SIAD and hypervolaemic hyponatraemia demonstrated a larger rise in plasma sodium concentration in response to tolvaptan than to placebo [11], and a later subgroup analysis confirmed that similar biochemical responses were consistent in the SIAD subgroup [12]. However, we still await the results of trials which compare the proven benefits of vaptans with first-line treatment with water restriction.It is therefore timely to see the results of an intervention study in SIAD patients in this journal [13]; the paper reported the effects of specialised endocrine care on outcomes in SIAD. The authors have a proven track record in the field, and as a group who have highlighted the poor ascertainment of basic diagnosti...