An unusual manifestation of a large bowel ischemia was observed in two patients. Both had a left flank tubular fluid collection demonstrated respectively by computed tomography (CT) and ultrasonography (US). At surgery, pyocolon (i.e. ischemic, dilated large bowel segments filled with pus) was discovered and resected. Pyocolon should be suspected in patients with ischemic colitis and sepsis. US, although useful, may be misleading; CT is the investigation of choice to establish the diagnosis.