Hyponatraemia is a common electrolyte imbalance in oncology. Rarely has it been reported as a presentation of nasopharyngeal carcinoma (NPC). A 43-year-old gentleman presented with double vision, headache, weight loss, complex ophthalmoplegia and submandibular lymphadenopathy. Computed tomography (CT) scan and nasopharyngeal biopsy confirmed the diagnosis of NPC. Prior to chemotherapy, he developed severe hyponatraemia. Blood investigations failed to pinpoint a clear diagnosis, and he was not responsive to aggressive supportive treatment. Pituitary gland function tests and MRI subsequently was performed, and found a pituitary extension causing hypocortisolism. Finally, his hyponatraemia was successfully optimised with oral hydrocortisone. This case illustrates that ophthalmoplegia and hyponatraemia are important warning signs of NPC or any other aggressive sellar mass that should not be neglected.