PURPOSE: To determine the isokinetic knee muscle strength and functional outcomes after medial patellofermoal ligament reconstruction (MPFL-R) in patients with patellar instability. METHODS: Seventeen patients with MPFL-R at one year after surgery and 17 controls were included in the study. The concentric isokinetic quadriceps and hamstring knee strength (at 60°/sec and 300°/sec) and knee joint position sense (at 20° and 60°) were evaluated with Biodex System 3. International Knee Documentation Committee and Kujala scores were used to determine the knee functional outcomes. The Mann Whitney U test was used to evaluate the differences between the knee muscle strength and JPS between patients with MPFL-R and controls RESULTS: The mean IKDC and Kujala scores were 85.2±16.8 and 58.4±11.5 at one year after surgery. The concentric quadriceps at 60°/sec (p=0.838) and 300°/sec (p=0.708) and concentric hamstring at 60°/sec (p=0.124) and 300°/sec (p=0.128) were similar between MPFL-R patients and controls. There were significant differences on JPS at 20° (p<0.001) and at 60° (p=0.003) between MPFL-R patients and controls. While the knee strength and the functional outcomes improved after one year following MPFL-R, the JPS results were poorer when compared with controls. CONCLUSIONS: The knee muscle strengthening and functional rehabilitation are essential after MPFL-R. The results showed that implementing the proprioception exercises into the rehabilitation programs is also important for MPFL-R patients.