Introduction Developmental dysplasia of the hip (DDH) is still a common and important disorder of childhood, with a prevalence of 0.1 to 2/1000 children. Using ultrasonography (US) in screening of DDH reduces the rates of open reductions and complications. In the current study, we aim to detect the optimal time for US examination for detecting DDH to prevent unnecessary repeating US examinations and treatments. Methods Children referred to US examination for a healthy child screening program, according to the health policy of our country, are included in the current prospective study. Both hips of each child were sonographically examined by the same radiologist using Graf's method at 4th, 8th, 12th weeks of life. Results A total of 2020 hips of 1010 children were examined. Fourth-week US results can predict 12th-week results (right hip: sensitivity 100%, specificity 75.7%; left hip: sensitivity 100%, specificity 78.3%). Eighth-week US results can predict 12th-week results (right hip: sensitivity 100%, specificity 87.5%; left hip: sensitivity 100%, specificity 83.9%). In predicting 12th-week US results, 8th-week results are found to be more successful than 4th-week results. Conclusions Late diagnosis of DDH might cause serious public health problems. On the other hand, early US examinations can result in false-positive diagnosis. Unfortunately, there is still confusion about the optimal time for DDH screening with US, especially among radiologists who are not specialized in DDH sonography. A US scan performed at eighth week of life can predict any pathology presence safely and correctly.