Omental cake refers to infiltration of the omental fat by material of soft-tissue density. Diffuse peritoneal and omental seeding are well-known forms of dissemination of metastatic carcinoma. The most common causes are metastases from the ovary, gastrointestinal tract or breast. We present a case of peritoneal carcinomatosis showing the appearance of caking on the PET/CT, with rising of CA-125, CA-153 and CEA. Ascitic fluid cytology suggested metastatic adenocarcinoma. The role of 18F-FDG PET/CT in diagnosing peritoneal carcinomatosis is discussed.