Castleman's disease (CD) appears at ubiquitous lymph nodes. To date, detection of the lesion focus for CD has mainly been carried out by physical examination and radiological findings, such as X-ray analysis, CT and MRI. 18F-FDG PET visualizes the active focus of glucose metabolism and the clinical value has been investigated for many different tumours. Previous studies of 18F-FDG PET for CD have only reported four cases of unicentric CD and no cases of multicentric CD. In this paper, we report two cases of CD, one with unicentric CD and one with multicentric CD. We demonstrate that the use of 18F-FDG PET for the detection and monitoring of patients with CD, especially multicentric CD, would be effective.