Background: The current management of displaced capitellum fractures is traditionally surgical. Most authors perform open reduction and internal fixation. The working hypothesis was that closed reduction and internal fixation of capitellum fractures is achievable by arthroscopy. Methods: We carried out a cadaveric study on six fresh frozen elbows. We performed two Bryan and Morrey type I fractures of the capitellum, three type II and one type IV using a 15 mm osteotome. Fracture reduction was performed under arthroscopy using a probe hook and an aiming femoral instrument set. Fixation with a lag screw was performed under arthroscopy and radioscopic control. We reviewed, two patients who had been operated on for a type I and type II capitellum fracture and osteosynthesized under arthroscopy with a 7.5 years follow-up. Results: In our cadaveric study, we obtained anatomical reduction and stable osteosynthesis in four cases. We had two failures (2 type II fractures) due to a fracture of the fragment during screwing. In our clinical study, range of motion was very satisfactory with only a 5° extension deficit. The x-rays did not reveal any signs of osteoarthritis or periarticular ossification. One patient had minimal signs of osteonecrosis. Conclusions: Arthroscopic osteosynthesis of capitellum fractures is feasible and reproducible. We recommend cannulated lag screws for Bryan and Morrey type I and IV fractures and adjustable lock pins for type II fractures. We have shown that this technique gives good results on two patients with a 7.5-year follow-up.