F-18-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) is routinely performed in oncology patients for various indications including staging, restaging, recurrence detection, and treatment response evaluation. Many disease- and treatment-related complications can be incidentally detected on PET/CT, which may be due to the complication of radiotherapy, chemotherapy, intervention, or primary tumor itself. Some of these complications could be life threatening and need urgent intervention. Therefore, these incidental findings should be recognized on PET/CT and immediately informed to the treating physicians if required urgent intervention.