Primary pituitary lymphoma in immunocompetent patients is a rare disease and has been described in less than 20 cases. Moreover, low-grade lymphomas constitute only 3% of all primary central nervous system lymphoma. The objective of this report is to report a low-grade primary pituitary lymphoma, diagnostic problems and to give more evidence about the evolution of this rare disease. A 49 y.o. woman was referred to our clinic with symptoms of hypopituitarism. A diagnostic work-up showed mild anemia, an erythrocyte sedimentation rate of 122 mm/h and a negative Elisa test for HIV. Panhypopituitarism was confirmed and the MRI showed a 20 mm sellar and suprasellar enhancing mass with a thickening of the pituitary stalk, chiasmal compression and bitemporal hemianopsia. She underwent transsphenoidal resection only 10 months later for non medical reasons. During this period she was clinically asymptomatic on hormonal replacement therapy. A new MRI showed regression of the suprasellar extension and invasion to the left cavernous sinus. A firm and infiltrative mass was found during transsphenoidal surgery, and only partial resection was performed. Biopsy showed a low-grade lymphoplasmacytic lymphoma. Staging was negative for other localizations. She was given chemotherapy and localized radiotherapy. Four years after surgery, the sellar MRI showed a 10 mm residual sellar mass with the persistence of a cavernous sinus invasion and she is considered to be in remission. The neurosurgeon and clinician should consider primary pituitary lymphoma as a potential cause of a sellar mass, especially in the presence of diabetes insipidus and an enhancing invasive mass. Neurosurgical biopsy is crucial for a correct diagnosis and prognosis could be better than classic CNS primary lymphomas.