Complications after arthroscopic surgery of the knee joint are infrequent. Quadriceps tendon ruptures after knee arthroscopy are rarities. Only two cases have been published in the medical literature. This article presents a case of a quadriceps tendon rupture that occurred in a 19-year-old patient 5 weeks after lateral release of the retinaculum by arthroscopy. The late occurrence differentiates this case from the other previously published cases.