There is controversy about the classification of Stevens-Johnson syndrome and toxic epidermal necrolysis. These rare but potentially debilitating dermatologic abnormalities have a mortality rate as high as 40%. The debate has centered on whether these conditions are related or separate entities. Current consensus is that they are variants of the same disease with differing severities, with the extent of epidermal detachment being the key component to its classification. A practical clinical classification considers less than 10% of the total body surface area involved to indicate Stevens-Johnson syndrome. If the epidermal detachment involves more than 30% of the total body surface area, then toxic epidermal necrolysis is the presumed diagnosis. An area between 10% and 30% is less definitive and is considered to represent Stevens-Johnson syndrome and toxic epidermal necrolysis overlap.