Though avulsion fracture of the fibular head rarely occurs, it frequently associates with lateral compartment injury of the knee which resulls in lateral instability. Some authors preferred to internally fixing avulsion fracture of the fibular head to prevent and restore lateral instability of the knee. Our purpose was to suggest that lateral instability of the knee be restored by internal fixation of the fibular head in these cases. We reviewed 6 cases of avulsion fracture of the fibular head associated with lateral instability of the knee which were treated surgically from January, 1993 to December, 1994 with average 2-year-over follow-up. We evaluated each cases using the Knee Ligament Standard Evaluation Form proposed by International Knee Documentation Committee. The results were as follows. The average displacement of the fibular head was 8.4mm. The activity level and overall grade were A(normal) in 4 cases, B(nearly normal) in 1 case, D(severe abnormal) in 1 case. Lateral instability of the knee was satisfactorily restored by internal fixation of the fibular head and repair of ligamentous injuries in cases of avulsion fracture of the fibular head associated with lateral instability of the knee.