Purpose:To follow children with a clubfoot by ultrasonography during the entire treatment period up to 4 years and compare with controls.Method:Thirty clubfeet in 20 children treated using the Ponseti method and 29 controls were followed by repeated ultrasonography investigations from neonates to the age of 4 years. The previously established coronal medial and lateral, sagittal dorsal and posterior projections were used. Changes over time, correlations to the Diméglio score, and the course of treatment were studied.Results:The medial malleolus–navicular distance was shorter, while the talar tangent–navicular distance and the talo-navicular angle were larger in clubfeet than in controls even after the initial correction. The healthy feet in unilateral cases did not differ significantly from the controls. The range of motion in the talo-navicular joint was approximately 20° less in clubfeet than in controls during the first four years of life. The medial malleolus–navicular distance (r= –0.58) and the talo-navicular angle (r= 0.66) at the first ultrasonography showed the highest correlation to the number of casts needed to correct the deformities.Conclusion:Ultrasonography can be used to evaluate the initial degree of deformities in clubfeet and to follow the progress of the treatment and growth. Ultrasonography showed a clear difference between clubfeet and controls during the first four years of life. Although it was not possible to define specific limit values as benchmarks in the treatment, dynamic ultrasonography can provide valuable support in the decision-making process when complementary treatment may be needed.Level of evidence:III