A multicenter international case-control study has been designed to elucidate 
the etiology of Stevens-Johnson syndrome and toxic epidermal necrolysis (TEN). 
Although these diseases occur rarely, the morbidity is high and the mortality 
for TEN is of the order of 30%. These serious dermatologic conditions have often 
been linked to exposure to drugs. Infective and autoimmune diseases, as well as 
other non-drug risk factors, have also been postulated to be of importance in 
increasing the risk. The design and methods are described, with particular 
attention to the unique challenges for an epidemiologic study of these 
conditions.