Retroperitoneal sarcomas are rare tumours. Although exceptional in the mesocolon, they can yet be considered as a special kind of retroperitoneal tumours. Leiomyosarcoma represents from 25 to 30% in this location. Clinical features are rarely obvious because the symptomatology depends upon displaced or compressed adjacent organs. Most authors agree on using the CT-scanner or MRI as diagnostic tools. However, the diagnosis is made after a histologic examination permitting the establishment of its grade and margins. Only a surgical treatment can offer prolonged survival and this can be improved if there is a low histological grade and total excision. The mesocolic location facilitates a radical removal and may therefore offer a better long-term prognosis.