The mortality of toxic epidermal necrolysis is about 30%. Our purpose was to develop and validate a specific severity-of-illness score for cases of toxic epidermal necrolysis admitted to a specialized unit and to compare it with the Simplified Acute Physiology Score and a burn scoring system. A sample of 165 patients was used to develop the toxic epidermal necrolysis-specific severity-of-illness score and evaluate the other scores, a sample of 75 for validation. Model development used logistic regression equations that were translated into probability of hospital mortality; validation used measures of calibration and discrimination. We identified seven independent risk factors for death and constituted the toxic epidermal necrolysis-specific severity-of-illness score: age above 40 y, malignancy, tachycardia above 120 per min, initial percentage of epidermal detachment above 10%, serum urea above 10 mmol per liter, serum glucose above 14 mmol per liter, and bicarbonate below 20 mmol per liter. For each toxic epidermal necrolysis-specific severity-of-illness score point the odds ratio was 3.45 (confidence interval 2.26-5.25). Probability of death was: P(death) = elogit/1 + elogit with logit = -4.448 + 1.237 (toxic epidermal nec-rolysis-specific severity-of-illness score). Calibration demonstrated excellent agreement between expected (19. 6%) and actual (20%) mortality; discrimination was also excellent with a receiver operating characteristic area of 82%. The Simplified Acute Physiology Score and the burn score were also associated with mortality. The discriminatory powers were poorer (receiver operating characteristic area: 72 and 75%) and calibration of the Simplified Acute Physiology Score indicated a poor agreement between expected (9.1%) and actual (26.7%) mortality. This study demonstrates that the risk of death of toxic epidermal necrolysis patients can be accurately predicted by the toxic epidermal necrolysis-specific severity-of-illness score. The Simplified Acute Physiology Score and burn score appear to be less adequate.