BACKGROUND: Developmental dysplasia of the hip is effectively treated with a Pavlik harness (PH) within the first 6 months of life. Over 80% of unstable hips in the newborn period will naturally stabilize by 2 months of age. If there is no difference in the effectiveness of initiating PH treatment at 1 week compared with 4 weeks of age, waiting may allow the hips to naturally stabilize and avoid treatment. The purpose of this study is to evaluate whether the timing of PH implementation influences its effectiveness in the treatment of developmental dysplasia of the hip. METHODS: A retrospective review was conducted between 2004 and 2010. Patients were included if PH therapy was prescribed for hip instability or dislocation at or before 6 months of age. PH failure was defined as requiring any operative procedure for definitive management. Groups were divided based on the age at which the PH was initiated-group1=<30 days, group 2=30 to 60 days, group 3=>60 days. RESULTS: A total of 176 children were included with 38 (21.6%) failing PH treatment. The mean age at PH initiation was 1.3 months (SD=1.3) in the successfully treated children and 1.4 months (SD=1.2) in the failures (P=0.77). There was no difference in the failure rates by age with group 1=19.1% (18/94), group 2=22.5% (9/40), and group 3=26.2% (11/42) (P=0.87). There was no statistical difference with respect to sex or breech positioning in the success or failure groups; however, there was a higher percentage of bilateral involvement in the failure group (P=0.04). CONCLUSIONS: Patients who had PH initiation before 30 days of age were no more or less likely to fail than when PH was initiated after 30 days of age. Parents can be counseled that waiting until after 30 days of age is appropriate before PH implementation. By avoiding swaddling during this period, the hips may stabilize without treatment and allow for more parental-infant bonding before implementation of PH. LEVEL OF EVIDENCE: Level III-therapeutic, case control study.