This study compared the Insall-Salvati (IS), Black-burne-Peel (BP), and Koshino-Sugimoto (KS) methods for measuring patellar malalignment in children. The IS and BP methods were inaccurate because the traditional landmarks for measurement were absent in the incompletely ossified pediatric knee. The KS method is based on the midpoint of the patella, the distal femoral physis, and the proximal tibial physis. The KS method applied to the extended knee was also inaccurate because of laxity in the patella ligament. However, the KS method applied to the flexed knee was the most accurate method for measuring patella malalignment in children.