Rectocolitis remains, at the present time, in spite of the large amount of work carried out, a condition of which the cause and the physiopathological mechanism are unknown: none of the theories proposed has been confirmed by the facts; none has made it possible to propose an effective therapeutic regimen. The diagnosis of haemorrhagic rectocolitis rests solely on an assembly of clinical, radiological, and anatomological findings, together with findings on progress of the disease; none of these findings taken separately being pathognomonic. Because of this it is essential in cases of inflammatory colic disorders to analyse critically these different elements before affirming the diagnosis that is often arrived at too easily. Different affections, even apart from Crohn's disease (parasitic, microbial, and iatrogenic affections, etc) may, in fact, give rise to radiological and clinical pictures close to those of haemorrhagic rectocolitis.