OBJECTIVE Enterogenous cysts (ECs) of the central nervous system are developmental malformations that occur in the spinal canal, posterior fossa, or cerebral hemispheres. They are usually benign lesions, and malignant transformation is rare. To date, only three cases of malignant transformation have been reported in the literature. We present a case of a cerebellopontine EC showing foci of epithelial dysplasia and malignant transformation into a low-grade papillary mucinous adenocarcinoma. METHODS A 25 year-old man with a 6-year history of hypoacusia presented to our department with facial nerve deficit, visual disturbances, and gait instability. A magnetic resonance imaging scan demonstrated a multiloculated cerebellopontine angle cyst with supratentorial hydrocephalus. METHODS A retrosigmoidal approach was used to achieve cyst removal. This was followed several months later by ventriculoperitoneal shunt placement. The cyst was adherent to the brainstem, cranial nerves, and vessels, and it resembled a thin encapsulated structure filled with mucinous-like substance. No solid component was identified. Histopathological examination revealed an EC with foci of malignant transformation in a mucinous papillary adenocarcinoma. Magnetic resonance imaging was performed 5 months postoperatively due to progressive clinical worsening; this scan revealed lesion recurrence with severe brainstem compression. Emergency surgery was performed, and a large decompression was achieved. Subsequent follow-up computed tomographic scans showed progression of the residual tumor. The patient's neurological condition rapidly worsened, ultimately resulting in death. CONCLUSIONS The present report suggests that a careful histological examination of all ECs after surgery should be made to exclude dysplastic foci or carcinomatous transformation. Although the clinical behavior of ECs with malignant transformation is unpredictable, surgery remains the treatment of choice. The use of possible adjuvant chemo- or radiotherapy has not been established.