Peritoneal diseases are common in clinical practice with a variety of causes, such as infective and malignant diseases. As a high-tech imaging technique, PET/CT examination can microcosmically observe the metabolic characteristics of the peritoneal lesions in addition to the morphological characterization. So it has great significance in early detection, differential diagnosis, and therapeutic efficacy observation of peritoneal diseases, as well as identification of the primary site of peritoneal metastasis. This paper presents the clinical value of PET/CT in the diagnosis of peritoneal diseases.