Abstract: Diffuse peritoneal lesions can be divided into two types, that include inflammatory and neoplastic diseases. The most common form of the former is tuberculous peritonitis. The most common malignant disease of peritoneal is metastatic tumor, followed by primary peritoneal tumors including peritoneal cancer, mesothelioma and lymphoma. Its differential diagnosis has been difficult in clinical work due to diffuse peritoneal lesions involve multiple kinds of diseases and their imaging features are extremely complex. The author selected two common cases of diffuse peritoneal lesions, which are tuberculosis of peritoneum and primary peritoneal cancer. We analyzed their clinical characteristics and imaging features of ¹⁸F-FDG PET/CT, in order to help with diagnosis and differentiation of the diffuse peritoneal lesions in clinical practice.