Peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) is an uncommon type of lymphoma with a clinically aggressive course and a relatively poor prognosis. Many affected patients present with nodal involvement, and there is also potential for extranodal involvement of the liver, gastrointestinal tract, bone marrow, and/or skin. We describe the case of a 68-year-old woman who presented with a 6-week history of an intermittently tender left-sided neck mass. Findings on imaging and fine-needle aspiration biopsy were inconclusive. Pathologic studies of excisional biopsy specimens ultimately revealed the diagnosis of PTCL-NOS. Of the lymphomas, neither PTCL nor the PTCL-NOS subtype is frequently discussed or studied in prospective trials. However, these cases should be identified because of their substantial clinical management implications.