Epidemiological studies of severe drug hypersensitivities are important to understanding the morbidity and mortality of this heterogeneous group of disorders. These insights also allow greater identification of at-risk patient groups. However, epidemiological studies of drug hypersensitivity reactions are challenging due to the variable diagnostic criteria applied and incomplete data sets studied. We review the epidemiology of severe drug hypersensitivity reactions with a particular focus on severe cutaneous adverse reactions (SCARs). SCAR diseases include: Stevens-Johnson syndrome, toxic epidermal necrolysis, drug rash eosinophilia and systemic symptoms, serum-sickness-like reaction and acute generalized exanthematous pustulosis.