Primary cutaneous lymphoma (PCL) is the second most common type of extranodal non-Hodgkin lymphoma, including both cutaneous T-cell and B-cell lymphomas. PCL comprises numerous subtypes and thus has myriad clinical presentations in the skin and subcutaneous tissues. Accurate classification and staging are important for making treatment recommendations for PCL and will further impact patient prognosis significantly. We review the role of fluorine-18-fluorodeoxyglucose (18F-FDG) PET (18F-FDG PET) and 18F-FDG PET with computed tomography (CT) in the diagnosis, staging, tumor biological evaluation, treatment response assessment, and early recurrence surveillance of PCL. Although 18F-FDG PET and PET/CT do not seem to adequately distinguish the plaque, patch, or erythroderma cutaneous lesions of PCL, the imaging modalities are superior to CT, MRI, and other nuclear medicine methods in detecting both the cutaneous and the extracutaneous lesions of PCL. The available literature addressing the clinical role of 18F-FDG PET and PET/CT in patients with PCL is promising for the use of the modalities in staging, tumor biological evaluation, biopsy guidance, early treatment response assessment, and recurrence surveillance. However, more data are needed to better specify the role of 18F-FDG PET and PET/CT in the management of PCL.