Down syndrome (DS) is a genetic disorder associated with mental and motor developmental delays in childhood. The aim of this study was to investigate the relationship of the femoral cartilage thickness with motor performance in children with Down syndrome (DS). A total of 39 children with DS in the age range of 12-42 months were included in the study (female/male: 21/18; mean age: 23.4 +/- 8.2 months). Femoral cartilage thickness was measured with ultrasound in the medial and lateral condyles and intercondylar areas of both knees. Gross motor subtest scaled scores of the Bayley Scales of Infant and Toddler Development III were used for the motor performance assessment. There was a positive correlation between the gross motor scaled scores and the femoral cartilage thickness in both knee joints (p < .05; r = 0.415 for the right medial condyle; r = 0.323 for the right lateral condyle; r = 0.339 for the right intercondylar area; r = 0.369 for the left medial condyle; r = 0.364 for the left lateral condyle, and r = 0.590 for the left intercondylar area). The study demonstrated that the femoral cartilage thickness was positively correlated with gross motor functioning in children with DS.