Aim:Facial nerve function is a quality of life determining factor in surgery for large vestibular schwannoma. To preserve facial nerve function, planned partial resection followed by stereotactic radiosurgery (SRS) is increasingly applied. Here, we contribute to this line of research by reporting our clinical and radiological outcome in a cohort of 23 patients with Koos 4 vestibular schwannoma. Material and Methods:Volumetric analysis of the tumour volumes before surgery, after surgery (before radiation), and at follow-up time-points after radiation was performed. Clinical data on facial nerve function and complications were collected. Approximately 6 months after surgery, all patients were treated with a single fraction of SRS using the Gamma Knife radiosurgery with a mean marginal dose of 12.9 Gy to the residual tumour volume. Results:Mean tumour volume was 11.64 cm3 which was reduced to a mean volume of 4.17 cm3 after partial resection. After a mean follow-up of 100 months, residual tumour showed a decrease in volume in 20 patients, stable disease in one patient and two patients showed progressive tumour volume requiring a second operation in one patient. Facial nerve function was preserved in all patients. One patient suffered from a trigeminal neuralgia after radiation. Conclusion:Planned partial resection followed by radiation for patients with Koos 4 vestibular schwannoma is an effective strategy to preserve facial nerve function and achieve tumour control. Residual tumours after planned partial resection showed a mean decrease in volume of 50% at the last follow-up time point.