Drug allergy is commonly encountered in clinical practice. It is an immunological response to a pharmaceutical agent. The clinical presentation can vary from mild cutaneous reactions to life-threatening conditions such as Stevens-Johnson syndrome and toxic epidermal necrolysis. Diagnosis is most often clinical, but investigations such as measurement of immunoglobulin E, patch testing, and skin biopsy may be required. In patients with a known drug allergy, the offending drug should be avoided.