We report the symptoms, clinical findings, and treatment of a patient with an extra-articular benign giant-cell tumor of the patellar ligament. Between the years 1966 and 1996 no similar case has been found to be documented by a Medline search. On palpation, a soft, mobile lesion, the size of a pigeon's egg, was felt in the lateral region of the patellar ligament. There was no set of laboratory values to determine the diagnosis. In addition, there were no typical findings in diagnostic imaging procedures and it seems that the most important fact is that the clinician is aware of this type of synovial tumor. A clear diagnosis is only possible by means of a pathological investigation. The choice of therapy for giant-cell tumors is local excision. Arthroscopy is recommended exclusively for the diagnosis and therapy of a localized intra-articular giant-cell tumor.