Objective:To prove that it is feasible to diagnoze discoid lateral meniscus in radiographs by analysis of plain radiographic findings of discoid lateral menisci with matched controls in a quantitative method.Methods:Total 122 consecutive patients,who were diagnosed with discoid lateral meniscus (discoid group)by magnetic resonance imaging(MRI)and arthroscopy,and 122 age-and sex-matched controls with normal medial and lateral menisci on the basis of MRI findings were included. Each plain radiograph was evaluated from the anteroposterior view for the following variables:height of the fibular head(A),lateral jointspace distance (B),height of the lateral tibial spine (C),obliquity of the lateral tibial plateau (α),obliquity of the lateral femoral condyle (β),distance from the lateral tibial spine to the lateralfemoral condyle (D),height of the medial tibial spine(E),chordal distance of the femoral condyle (F,G),the A/B,B/C and the F/G. Statistical analyses were used to determine the differences between the two groups. Results:A significant difference was found in the A,B,C,D,F,A/B and B/C between the two groups. The difference in cut-off values of A/B and B/C was most significant. At the same time,the roc curve area of the A/B and B/C ranked highest among all the results. Conclusion:There were significant differences in the variables,especially the A/B and the B/C,between plain radiographic findings of discoid lateral meniscus patients and normal controls. The results of the A/B and the B/C showed a positive impact on the diagnosis of discoid lateral meniscus in this research. These findings enable radiographs to screen for discoid lateral meniscus.