We report a case of a 15-year-old boy with desmoplastic medulloblastoma of the posterior fossa (T3M3, according to Chang classification) incompletely resected, with leptomeningeal and nodular spread in the posterior fossa and in the cervical and thoracic tracts of the spine, treated with sequential high dose iv chemotherapy and with hyperfractionated cranio-spinal radiotherapy. While on maintenance chemotherapy, the boy developed fever and septic status caused by Pseudomonas aeruginosa, and 1 week later also low back pain. Magnetic resonance imaging (MRI) demonstrated abnormal signal in the fourth ventricle and in the dorso-lumbar tract suggesting medulloblastoma recurrence, so he started with a chemotherapy program. Due to a worsening of back pain, a second MRI of the spine was performed that showed a spondilodiscitis of T11-T12 and L1-L2 discs. The histological and cultural examination of a fine-needle biopsy of the L1-L2 disc revealed the presence of P. aeruginosa. So patient was treated with intensive antibiotic therapy with resolution of the infection. Spondilodiscitis is a rare complication in neoplastic patients, maybe due to either immunodeficient status or invasive procedures such as lumbar puncture. This case demonstrates that MRI is a useful method for differentiating between infection and malignancy in the spine, but sometimes it may be difficult to distinguish metastatic tumor from a lesion due to spondilodiscitis. In this case surgicopathological assessment is crucial and mandatory.