Adalimumab is a fully human chimeric tumor necrosis factor inhibitor used to treat immune-mediated disorders such as psoriatic arthritis. We present a 51-year-old woman with psoriatic arthritis on methotrexate and infliximab for 12 years. Adalimumab replaced infliximab because of worsening symptoms. Following 3 doses administered 1 week apart, rapidly enlarging cervical lymph nodes developed. Biopsy revealed Epstein-Barr virus-related polymorphic lymphoproliferative disorder. F-FDG PET/CT demonstrated widespread hypermetabolic lymphadenopathy; follow-up at 5 weeks off adalimumab revealed almost complete resolution of this adenopathy. This is most consistent with Epstein-Barr virus-related lymphoproliferative disorder secondary to tumor necrosis factor α inhibition.