The diagnosis and assessment of severity of acute colonic diverticulitis may be difficult. A case is presented, in which the delayed diagnosis of diverticulitis resulted in the development of a diverticular mesocolic abscess complicated by hepatic-portal venous gas (HPVG). The utility of ultrasound as a rapid, noninvasive tool to diagnose this distinctly rare condition is outlined. The literature on HPVG associated with acute colonic diverticulitis is reviewed, and the therapeutic options are discussed.