We present a recently discovered paper that witnesses to arthroscopic activity before World War I. The Proceedings of the 4lst Congress of the German Society of Surgeons at Berlin in 1912, contain a presentation entitled "Endoscopy of Closed Cavities by the Means of My Trokart-Endoscope." The author was a Danish surgeon from Aarhus named Severin Nordentoft. Dr. Nordentoft had constructed an endoscope similar to the Jacobaeus thoracoscope, consisting of a trocar 5 mm in diameter, a fluid valve, and an optic tube. In addition to suprapubic cystoscopy and laparoscopy, he advised the use of such an endoscopic device in the knee joint, especially for early detection of meniscal lesions. He baptized the procedure "arthroscopy" and gave a vivid and credible description of the handling of the instrument, and the view of the anterior region of the knee, including the articular cartilage, synovial lining, villi, and plicae. He used sterile saline as the optical medium. Unfortunately, he did not express clearly if he performed arthroscopy on patients or on cadaver knees. This is the only known paper or presentation by Severin Nordentoft on the topic of arthroscopy. In the following years, his interests changed to radiotherapy, and today Danish radiologists remember him as a pioneer in x-ray treatment of mammary carcinoma and brain tumors. Although his pioneering work in arthroscopy was overlooked, the primacy of this procedure must now be attributed to him.