Juvenile pilocytic astrocytoma is a well-defined brain tumor. It most often occurs in children and young adults. It is located in the posterior fossa and has typical imaging features, associating cystic and strongly contrast enhancing mural nodule. After complete surgical removal, its prognosis is excellent. Adult cases are seldom observed. They develop almost exclusively within the cerebral hemispheres and share the same imaging and prognostic characteristics as the pediatric forms. We describe the case of a 42-years-old man presenting with a huge heterogenous posterior fossa lesion. Histopathological analysis of the lesion after surgical resection diagnosed a juvenile pilocytic astrocytoma. These peculiar location and imaging features in an adult patient may be misdiagnosed for infectious lesions and must be recognized.