We present the case of a young woman who suffered from acute lymphatic leukaemia when she was 8 years old. She was treated with bone marrow transplantation and intrathecal chemotherapy. The girl recovered and was considered disease-free. The Ommaya-reservoir and catheter to the ventricle in the right frontal lobe were left in situ. Twenty years later, a tumour was diagnosed that was located around the catheter. Histology disclosed an anaplastic oligo-astrocytoma WHO III.