Congenital agenesis of the right lobe of the liver in situs ambiguous is rare. This abnormality revealed by a colonic obstruction due to a wandering spleen torsion has never been described. We report the case of a young man admitted for acute colonic obstruction associated with a painful hypogastric mass. Plain abdominal X-ray showed an enormous colonic dilatation with a soft-tissue density imaging in the lower middle quadrant. Laparotomy found a colonic obstruction due to pedicle torsion of a wandering spleen around the sigmoid. The liver was located at the left hypochondrium and presented a congenital agenesis of the right lobe with a retrohepatic gallbladder. The patient underwent splenectomy and sigmoidectomy. Liver and gallbladder were respected. The post-operative course was uneventful. This case presentation highlights the necessity to diagnose liver and other organ abnormalities in situs ambiguous earlier in order to prevent acute complications and to survey hepato-biliary patterns.