Invasive peritoneal disease includes more than just peritoneal carcinomatosis. Although this is the most common aetiology, especially when a primary is found, other conditions may be responsible for peritoneal invasion. A rigorous analysis of CT features taken together with the clinical and biological context usually allows the main differential diagnoses, which entail different types of management, to be drawn out. Pseudomyxoma peritonei, peritoneal lymphomatosis, tuberculosis, peritoneal mesothelioma, diffuse peritoneal leiomyomatosis, and benign splenosis are the main differential diagnoses.