Abstract
The giant cell tumour of the tendon sheath (GCTTS) is the second most common soft tissue benign tumour and rarely presents in the knee. We report a rare presentation of a GCTTS in the knee with corresponding magnetic resonance imaging (MRI), an arthroscopic picture, and histological presentation. It is a rare occurrence but should be considered as a differential in atraumatic knee pain presentation. This case report gives a classic picture of its presentation, diagnosis, and histopathology.