Objective: Presenting a case operated for an arachnoid cyst localized in posterior fossa.

Methods: A 52 year-old male patient presented with the complaints of severe headache, occasional nausea and loss of balance going on for two years was investigated.

Results: Cranial MRI of the patient, whose neurological examination was found to be normal, depicted a cystic lesion of 4.5 x 3 x 3 cm which compressed and constricted the fourth ventricle in inferior cerebellar vermis, compressed bulbus in the posterior, caused slight hydrocephalic expansion with no contrast enhancement. Through the Cranial MRI Spectroscopy and Diffusion MRI investigations conducted for a distinctive diagnosis, the lesion was detected to resemble an arachnoid cyst. Operated upon these findings, the patient went under suboccipital craniectomy as well as excision and fenestration of cystic wall

Conclusion: Posterior fossa arachnoid cysts can either be asymptomatic or cause non-specific symptoms. Surgical treatment indications and methods for such cysts are still a matter of discussion. An adult posterior fossa arachnoid cyst case, which was operated at our clinic and had a follow-up period of one year, was presented and discussed in the light of literature.

Keywords: Arachnoid cyst, posterior fossa, surgery, treatment