Lymphoma involving the pituitary gland is very rare and usually results from metastatic spread of systemic lymphoma. We present a case of primary central nervous system (CNS) large B cell lymphoma that manifested as pituitary apoplexy. A 45-year-old woman presented with headache, and then rapidly developed a third nerve palsy and bitemporal hemianopsia. Imaging suggested a pituitary macroadenoma, with spontaneous necrosis, extending into the suprasellar region, compressing the optic chiasm and invading the right cavernous sinus. The patient underwent transsphenoidal resection which revealed a vascular, firm tumor. An aggressive decompression of the optic chiasm was performed with complete resolution of both visual fields and third nerve palsy. Final pathology showed B cell lymphoma. Systemic work-up including bone marrow aspiration and CSF studies showed no other foci of lymphoma, and the patient was HIV-negative. Chemotherapy with methotrexate, vincristine, procarbazine, and dexamethasone was administered for primary CNS lymphoma. This is an uncommon diagnosis of which the clinician should be aware in order to tailor surgical intervention and provide early institution of proper therapy.