The formation of a cervical spinal cord syrinx as a result of an infratentorial mass, even though uncommon, has been reported in international literature. In such cases, syringomyelia is usually asymptomatic, while the tumour-related symptoms and signs predominate. We report a patient with a posterior fossa tumour and secondary syringomyelia. In this patient, syringomyelia symptoms and signs were present, and a cervical spine Magnetic Resonance Imaging (MRI) showed a large cervical syrinx. A more careful clinical examination though, revealed a sub-clinical posterior fossa syndrome and brain MRI revealed a large infratentorial meningioma. A posterior fossa craniotomy was performed, followed by complete tumour resection and almost complete remission of the syrinx and its related symptoms. The authors discuss the role of posterior fossa tumour induced tonsillar herniation in the development of secondary syringomyelia, the mechanisms leading to syrinx formation and the conditions that must be fulfilled for that to happen.