This case-report studies the clinical, radiological, anatomopatholo-gical and therapeutic aspects of peripheral primitive neuroectodermal tumours (PNET). PNET are neoplasms with a similar histology to tumours in the Ewing family. Diagnosis requires histopathology, immunohistochemistry and cytogenetic studies. To our knowledge, this rare tumour has never been reported in the mesocolon (our case). The treatment, which is usually similar to that for Ewing's sarcoma is complex and has not yet been codified, which is another difficult aspect of this disease with a poor prognosis.