Medulloblastomas are malignant primitive neuro-ectodermal neoplasms of childhood. In adults, clinical manifestations, imaging and prognosis can be different from that observed in children. Three adult patients with confirmed diagnoses of medulloblastoma are discussed in this report. They presented with unusually prolonged clinical courses and with imaging more suggestive of L'hermitte-Duclos disease. Medulloblastoma should be considered in all adults with posterior fossa masses despite having clinical and radiological features suggestive of a low-grade tumour. Definitive diagnosis requires histological confirmation in all cases.