Introduction: In-hospital hypernatremia is associated with increased mortality rates. We want to elucidate the impact of in-hospital acquired hypernatremia in mortality of Toxic Epidermal Necrolysis (TEN). Purpose: Is there an association between hypernatremia and mortality in patients with TEN? Method: Retrospective study of 25 patients with TEN. Laboratory electrolyte results, diuresis and survival were analyzed. Patients were separated in two groups without (Group A) or with (Group B) hypernatremia. Results: In Group A 10 patients with a TBSA of 74±25% (mean ± standard deviation), and a SCORTEN-Score of 2.7±0.9 were summarized. Diuresis within the first 10 days after admission was 1±0.3 ml/kg/hour. In Group B 15 patients with a TBSA of 76±19%, and a SCORTEN-Score of 3.5±1 were included. Diuresis within the first 10 days after admission was 1.4±0.4 ml/kg/hour. Hypernatremia occurred on day 3.3±2.4 after admission and persisted for 5.3±2.9 days. Statistical analysis showed a significantly higher diuresis (p=0.007) and SCORTEN-Score (p=0.04) in the hypernatremic patients. One normonatremic and 8 hypernatremic patients died during ICU-stay (overall mortality rate 36%). A significantly higher mortality rate was found in Group B (odds ratio: 13,5; 95% confidence interval: 1.34-135.98; p=0.01) during ICU-stay. Conclusion: TEN patients with an in-hospital acquired hypernatremia have an increased mortality risk. Close electrolyte monitoring is advisable in these patients.