We report on 9 patients with persistent ankle pain and radiographic evidence of a cystic lesion on the talus. All had a history of an inversion-type of ankle injury. Radiographs were initially negative, but a cyst developed about 6 months after the injury. Arthroscopic debridement revealed extrusion of viscid gelatinous material from the cyst. The cavity was arthroscopically abraded to bleeding base. Follow-up of these patients at an average of 26 months showed statistically significant improvement in terms of pain, swelling, stiffness, limp, and activity level. Bone grafting may not be necessary in the treatment of post-traumatic cysts.