CRP and infection: Well-described complications of polyetheretherketone (PEEK) cranioplasty in pediatric patients include surgical site infection, post-operative hematoma, cerebral edema, and implant fracture. We present a rare case of hypersensitivity to PEEK presenting as an epidural effusion in a 7-year-old male receiving a PEEK cranioplasty following a decompressive craniectomy. Within three weeks, the patient experienced fever and emesis. Erythrocyte sedimentation rate (ESR) was high (>130 mm/Hr) as well as C-reactive protein (CRP) (6.4 mg/dL).