The Centers for Medicare and Medicaid Services coverage includes 3 posttherapy F-18-FDG PET/CT scans per patient and per tumor type. Any additional follow-up F-18-FDG PET/CT scans will be reimbursed at the discretion of a local Medicare administrator, if deemed medically necessary. This study aimed to investigate common clinical indications for performing a fourth or additional followup 18F-FDG PET/CT scans that could affect the management of patients. Methods: This was a retrospective institutional review of 433 oncology patients (203 men; mean age, 55 y), including a total of 1,659 fourth or subsequent follow-up PET/CT scans after completion of primary treatment. Twelve indications for performing a fourth or subsequent follow-up PET/CT scan were determined, and the impact of each of the 12 indications on patients' management was evaluated. Results: The primary tumors were breast cancer (92 patients, 426 scans), non-Hodgkin lymphoma (77 patients, 208 scans), Hodgkin disease (41 patients, 182 scans), colorectal cancer (70 patients, 286 scans), melanoma (69 patients, 271 scans), and lung cancer (84 patients, 286 scans). The indications were categorized in 4 groups: PET/CT for diagnosis of tumor recurrence (303/1,659, 18.3%), PET/CT before starting therapy for tumor recurrence (64/1,659, 3.9%), PET/CT to assess therapy response for tumor recurrence (507/1,659, 30.6%), and follow-up PET/CT after completion of treatment for tumor recurrence (785/1,659, 47.3%). Overall, fourth and subsequent follow-up F-18-FDG PET/CT scans resulted in change in management in 31.6% of the scans (356 of 1,128) when the scans were obtained for medical necessities (indications 1-11), and in 5.6% of the scans (30/531) when the scans were obtained without any medical necessity (indication 12). Conclusion: The fourth and subsequent PET/CT scans obtained after completion of primary treatment led to a change in management in 31.6% of the scans when acquired for appropriate clinical reasons. Performing follow-up PET/CT without appropriate medical reason had a low impact on patients' management and should be avoided.