This research was done in the Asan Medical Center in Seoul. We performed a prospective study to assess clinical outcomes, complications and survival of prostheses in a consecutive series of 278 knees receiving NexGen legacy posterior stabilised (LPS) – Flex total knee replacement (TKR) between May 2003 and February 2005. The mean follow-up period was 3.8 years (3.0 to 4.8), and 259 knees (93.2%) were followed for an adequate interval. Annual follow-ups showed improvement in the Knee Society scores (paired t-test, P< 0.05). At the latest follow-up, the mean maximal flexion was 135° (110° to 150°). Two knees showed radiolucency but revision was not required as there were no significant symptoms. Revision was required in one case due to prosthetic infection, but no prosthesis-related revisions were required. There were no complications such as patellofemoral pain, wound healing problems, dislocation or instability during deep flexion postoperatively. The estimated survival rate at 4 years with revision for any reason and prosthesis-related problems were 99.6% and 100% respectively (life-table method). This relatively large TKR study indicates that LPS-Flex system provides excellent medium-term outcomes and seems to warrant ongoing evaluation to confirm the long-term durability and functioning of the implant afterward.