Measurements were taken and statistically analyzed from the initial radiographs, the 1-year follow-up radiographs, and the most recent radiographs of 81 patients (103 hips) to determine which measurements could predict the success of treatment. The average follow-up was 49 months (range, 12-139 months), and the average age of the patients at the last follow-up was 65 months (range, 15-190 months). Analysis of the data showed that the measurement with statistically significant predictive value was the Tonnis grade of dislocation determined from the initial radiograph. A single unit increase in the Tonnis grade was associated with a doubling of the odds of failure in patients treated with a Pavlik harness (P < 0.04, odds ratio = 2.2) or a closed reduction (odds ratio = 2.0).