We report the case of a 13-year-old boy with bilateral osteochondritis dissecans in the lateral femoral trochlea of the knees. They were classified as grade 4 in the right knee and grade 1 in the left knee on the basis of the Nelson classification within 1 year after first consultation. In the right knee, the fragment was surgically fixed, but the left knee healed with conservative treatment. This case indicates the possibility that osteochondritis dissecans of the lateral femoral trochlea may develop bilaterally at different times and present at different stages. The case shows the importance of early diagnosis and appropriate treatment on the basis of the stage.