Lymphoma is one of the causative factors of hypothalamus–pituitary dysfunction, and intravascular large B-cell lymphoma (IVLBCL) is a subtype of primary extranodal neoplasm. A 69-year-old woman visited our hospital because of general fatigue. We diagnosed her with presumable non-functional primary pituitary adenoma and subsequent dysfunction. Eight months after, the patient revisited our hospital because of dyspnea. Though we conducted systemic investigations including chest and abdomen enhanced computer tomography, transbronchial lung biopsy, and bone marrow biopsy, the diagnosis was not confirmed. Inadvertently, a breast cancer was found, and the surgical specimen proved that the patient had double cancer—adenocarcinoma and IVLBCL. Rituximab, cyclophosphamide, adriamycin, vincristine, and prednisolone regimen was initiated, and complete remission was achieved. Notably, the sellar mass returned to normal size with improved function. We reviewed 32 patients with primary parasellar lymphoma. In affected sites, both sellar and pituitary stalk (6.7%), both hypothalamus and pituitary stalk (6.7%), only sellar (63.3%), only pituitary stalk (6.7%), only hypothalamus (13.3%), and only clivus (3.3%) were observed. In hypothalamus–pituitary dysfunction, both anterior and posterior dysfunction (20.7%), only anterior dysfunction (58.6%), only posterior dysfunction (3.4%), and no dysfunction (17.2%) were observed. It seemed that hypothalamic lesion is related to both anterior and posterior dysfunction, while sellar lesion is related to mainly anterior dysfunction. In cranial nerve dysfunction, 2nd nerve dysfunction (45.2%) and 6th nerve dysfunction (35.5%) were frequently observed. It seemed that sellar lesion is related to both 2nd and 6th nerve dysfunction, while hypothalamic lesion is related to mainly 2nd nerve dysfunction.