A 55-year-old Caucasian woman with a previously documented sulfa allergy was admitted to the hospital after she developed toxic epidermal necrolysis; she had been taking valdecoxib for 8 days for knee pain. Four days later, her bullous lesions had progressed to 45-50% of her body surface area. She was transferred to a burn unit for aggressive wound care and fluid hydration. Valdecoxib, a cyclooxygenase-2 inhibitor, is a benzenesulfonamide prescribed for arthritis pain and inflammation, and dysmenorrhea. Clinicians should exercise caution when prescribing valdecoxib to patients who are allergic to sulfa drugs.