The purpose of this study was to evaluate the early radiological outcome after ultrasound-monitored treatment of developmental dysplasia of the hip (DDH) and to examine whether there was a correlation between the initial severity of DDH, measured by ultrasound, and the severity of residual dysplasia on the radiograph at the first follow-up. At the beginning of ultrasound-monitored treatment, the sonographic findings of 90 children (72 girls, 18 boys, mean age 7.2 weeks) with DDH (29 unilateral, 61 bilateral) were staged according to the Graf classification and assigned to four categories. Treatment was continued until normal ultrasound findings were reached. At the time children started walking (mean age 14.8 months), an anteroposterior radiograph of the pelvis was performed. The acetabular index was measured and classified according to the normal values of the hip joint, as described by Tönnis. The ultrasound findings expressed by the Graf classification were compared with the acetabular index measured at radiographic follow-up. Although normal values in ultrasound were reached before abduction splinting was discontinued, at the time of radiological follow-up, 59 hips (32.8%) showed mild residual dysplasia and another 53 hips (29.4%) showed severe residual dysplasia according to the criteria of Tönnis. Statistically, there was no significant correlation between the Graf classification and the radiological outcome at follow-up. Even after successful ultrasound-monitored treatment, a risk for residual dysplasia remains. Therefore, radiological follow-up of every hip treated once is necessary. We found no correlation between the severity of DDH measured by ultrasound and the subsequent presence of residual dysplasia at radiological follow-up.