Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma and comprises approximately 30% of all lymphomas. Patients typically present with a nonpainful mass in the neck, groin, or abdomen associated with constitutional symptoms. In this report, however, the authors describe a rare case of a 61-year-old woman with hyperprolactinemia, hypothyroidism, and acromegaly (elevation of insulin-like growth factor-1 [IGF-1]) with elevated growth hormone–releasing hormone (GHRH) in whom an MRI demonstrated diffuse enlargement of the pituitary gland. Despite medical treatment, the patient had persistent elevation of IGF-1. She underwent a transsphenoidal biopsy, which yielded a diagnosis of DLBCL with an activated B-cell immunophenotype with somatotroph hyperplasia. After stereo-tactic radiation therapy in combination with chemotherapy, she is currently in remission from her lymphoma and has normalized IGF-1 levels without medical therapy, 8 months after her histopathological diagnosis. This is the only reported case of its kind and displays the importance of a broad differential diagnosis, multidisciplinary evaluation, and critical intraoperative decision-making when treating atypical sellar lesions.