Background: The rate of spontaneous normalization in type IIa hipsis reported to be high, whereas dysplsia persists or worsens in 5%-10% of cases.Aims: To evaluate the natural course of type IIa hips using Graf’sown perspective of physiological immaturity and maturational deficit.Study Design: A single center, retrospective cohort study.Methods: This was an institutional review board-approved retrospectivereview of all patients diagnosed with type IIa hip dysplasia at a singleinstitution from 2012 to 2014. All patients included in the study hadhip ultrasonography at about 6 weeks and 3 months of age. To assessreliability in α and β angles, ultrasonography measurements werecarried out on the same image individually by all observers. The α andβ angles were used as the main outcome measurements to evaluate hipmaturation at the last follow-up. A receiver operating characteristicscurve was drawn at the 3 month ultrasonography to evaluate the cut-offvalues for α and β angles for persistent dysplasia.Results: Sixty-four patients and 88 affected hips (63% unilateral and37% bilateral) were included. The mean age at diagnosis was 6.4±2.7weeks. Fifty-four hips were type IIa(+) (physiologically immature)and 34 hips were type IIa(-) (maturational deficit) at the initialultrasonography evaluation. Improvement to type I was seen in 52type IIa(+) and 17 type IIa(-) hips. Receiver operating characteristicanalyses showed that patients do well if the α angle was >55° (areaunder the curve: 0.86; p<0.001 for the left hip and area under thecurve: 0.72; p=0.008 for the right hip).Conclusion: The cut-off α angle value of 55° on initial ultrasonographyshould be considered to prevent future dysplasia. An α angle <55° onthe initial ultrasonography was an independent predictor of worseningsonographic findings.