Objective To investigate individual variations of the femoral isometric poiIit of anterrior cruciate ligament(ACL). Methods The femoral isometric points(i)were determined by measuring the knee joint lateral projections in 100 adults.The distances from the femoral isometric point i to the posterior border of intercondylar notch were measured and compared among 4 age groups(20 to 30 y,30 to 40 y,40 to 50 y and>50 y)by 2 × 2 factor analysis and Student-Newman-Keuls (SNK-q)Analysis to determine the effects of age and gender on the measurements. Results The average distance was(10.6±1.55)mm,ranging from 15.05 am to 7.50 mm.The 2×2 factor analysis showed the differences were signifcant between age groups(F=2.843,P=0.042)and between sexes(F=4.245,P=0.042).but the age and sex factors were not interacted (F=0.456,P=0.7 14). The SNK-q Analysis revealed the differences were significant between the 20 to 30 y group and the 40 to 50 y group as well as the>50 y group(P<0.05),but not significant between the 30 to 40 y group and the 20 to 30 y group(P>0.05).No signifieant difference was observed between any two of the 30 to 40 y group,40 to 50 y group and>50 y group(P>0.05). Conclusion Since the ACL femoral isometric points vary from person to person,it is valuable to check them twice radiologically before and during the operation.