INTRODUCTION: Since there are no valid tools available for the diagnosis of Complex Regional Pain Syndrome I, exclusion of other underlying conditions plays an important role in the diagnostic process. CASE PRESENTATION: A 77-year-old Caucasian man was referred with painful swelling and dysfunction of the right knee. Based on the history and clinical presentation, the referring physician assumed a case of Complex Regional Pain Syndrome I. However, after careful evaluation of the differential diagnosis, a metastatic urothelial carcinoma was diagnosed. CONCLUSION: Even if the clinical picture resembles Complex Regional Pain Syndrome I, the differential diagnosis must be evaluated carefully.