A patient can be allergic to a new knee and such allergy is an often-overlooked complication of prosthetic implant surgery. Here, Fogel et al present their assessment, diagnosis and management of a 60-year-old woman who presented to their dermatology clinic with a pruritic, crusted rash on her right knee. Eighteen months earlier, she had undergone a right knee replacement with an Evolution Medial-Pivot knee system. No complications occurred, and the patient had normal healing at the surgical site. Her past medical history was notable for conditions within the atopic diathesis, including severe asthma, sinusitis, postnasal drip, and a childhood history of eczema. In addition, she reported allergies to medications, including lisinopril and epineph rine. A review of systems was otherwise unrevealing.