In this study, we present a case of a very rare and large suprapatellar synovial cyst of the knee, which was successfully treated with an arthroscopic intra-articular decompression. Suprapatellar bursa is located between the femur and quadriceps tendon, proximal to the knee joint, and it normally communicates with a joint cavity. However, very rarely bursa can remain completely separated from the knee joint, which can result in the formation of a separated compartment inside which, in special circumstances, fluids can be accumulated and with time can lead to the formation of suprapatellar cyst. Although certain authors use ultrasound, arthrography and computerized tomography, MRI is recognized as the 'gold standard' in diagnostics of knee cysts. When considering ways of treatment, according to the available literature, suprapatellar cysts are treated mostly by an open excision, whereas in our case we managed to show that cysts could also be effectively and safely treated by arthroscopic decompression, with no recurrence and followed by fast and functional recovery.