A 47-year-old woman developed allergic contact dermatitis (ACD) to a knee brace after anterior cruciate ligament repair, manifesting as numerous erythema multiforme-like lesions. No previous cases of ACD to this Townsend Rebel knee brace, which is commonly worn postoperatively, have been reported. The patient was treated with triamcinolone ointment, cetirizine, and diphenhydramine. On follow-up, the lesions had resolved. We share this case to increase knowledge of this reaction pattern and encourage further similar reports to clarify the nature of the reaction.