Introduction CSF leak is a rare complication of macroprolactinomas. It almost always follows initiation of medical management, whereby tumour shrinkage exposes a sellar defect, or surgery. Presentation with CSF leak prior to any therapy is extremely rare. We present a case of a macroprolactinoma presenting with de novo CSF leak, with multiple post-operative recurrences. Case Presentation A 26-year-old male weighing 224kg presented to ENT outpatients with 2 years of intermittent rhinorrhoea and headache. Nasendoscopy showed a visible posterior nasal tumour and the fluid was β2-transferrin positive. CT Sinuses demonstrated a large base of skull erosive lesion with a sellar and suprasellar component (34x26x16mm) involving the right clinoid and sphenoid sinus with cavernous sinus invasion; due to elevated BMI, MRI could not be performed. The patient was commenced on Cabergoline and underwent endoscopic endonasal debulking with multilayered repair utilising fascia lata, fat, and nasoseptal flap. He was well for 7 weeks, but then presented 5 times in 5 months with recurrent leak. Initial relook demonstrated extensive tumour necrosis disrupting the repair, however 2 further relooks did not highlight a leak. The patient proceeded to LP shunt and remained well at his most recent follow-up. Discussion CSF rhinorrhoea is a rare complication of macroprolactinoma; only in extremely rare cases is it the presenting symptom. A combination of delayed presentation, large tumour size, and tumour shrinkage with medical therapy most likely resulted in this patient’s recurrent leak. References 1.Javed, Zanib et al. “Invasive pituitary adenoma presenting with cerebrospinal fluid rhinorrhea and meningitis - A case report.” Surgical neurology international vol. 15 318. 6 Sep. 2024, doi:10.25259/SNI_224_2024 2.Patel, Aneek et al. “Spontaneous Cerebrospinal Fluid Rhinorrhea from a Prolactin-Secreting Pituitary Macroadenoma.” Cureus vol. 13,2 e13111. 3 Feb. 2021, doi:10.7759/cureus.13111