Objective To analyze the imaging manifestations of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography （¹⁸F-FDG PET/CT） in the patients with pleural and peritoneal mesothelioma， and to enhance the diagnostic accuracy for this disease. Methods A retrospective analysis was conducted on the ¹⁸F-FDG PET/CT imaging and immunohistochemical results of 22 patients confirmed pleural and peritoneal mesothelioma （21 malignant and 1 benign） by pathology. The imaging features and glucose metabolism characteristics were summarized. Results The majority of the patients with malignant pleural mesothelioma presented with unilateral pleural diffuse thickening accompanied by increased radiotracer uptake， and the thicknesses were ranged from 1.0 to 10.6 cm and the average semi-quantitative maximum standard uptake value （SUV_max） was 10.1. Over half of these patients also had a small amount of pleural effusion. The patients with malignant peritoneal mesothelioma mostly showed diffuse thickening of the peritoneum， omentum， and mesentery with increased radiotracer uptake， and the thicknesses were from 1.2 to 6.6 cm and the average SUVmax was 8.4， and over half of these patients had a significant amount of abdominal ascites. Besides the primary sites， nodular， striated， and mass-like abnormal radiotracer uptakes were observed in other metastatic sites in 17 cases of malignant mesothelioma， suggesting metastasis， and the average SUV_max was 7.4， predominantly surrounding lymph node metastasis. Bone and muscle metastases were visible in the patients with malignant pleural mesothelioma， while no such metastasis were seen in those with malignant peritoneal mesothelioma. One patient with benign pleural mesothelioma presented with bilateral pleural diffuse thickening approximately 3.5 cm thick， without significant abnormal radiotracer uptake and with a minor pleural effusion. Conclusion The ¹⁸F-FDG PET/CT imaging manifestations of pleural and peritoneal mesothelioma exhibit the distinctive characteristics. The mode and thickness of pleural and peritoneal thickening， the presence and degree of ¹⁸F-fluorodeoxyglucose uptake， can preliminarily differentiate between benign and malignant mesothelioma， thus providing valuable references for the early clinical diagnosis of mesothelioma. PET/CT based on whole-body imaging can determine whether there are other sites of metastasis， which is helpful for clinical staging.