Purpose Early detection and conservative treatment are essential for a successful outcome in developmental dysplasia of the hip (DDH). The aim of this study was to evaluate the efficacy of Tubingen hip flexion splint treatment on dislocated hips of type D, 3, and 4 according to the Graf classification. Methods A total of 104 dislocated hips in 92 patients were treated with Tubingen splints. Splint treatment was applied to patients with dislocated hips as diagnosed under ultrasonographic evaluation. After four to six weeks of treatment, the hips were re-evaluated according to the Graf classification under ultrasonography. The success of Tubingen splinting was determined as follows: hips initially diagnosed as Graf type 3 and 4 were upgraded to type 2c, 2b, or 1 after treatment, and hips initially diagnosed as Graf type D were upgraded to type 2b or 1 after treatment. Results The mean age at treatment initiation was 11.91 +/- 5.16 (range, 4-32) weeks. There were no statistically significant relationships between success rates and sex, bilateral hip involvement, or initial physical examination findings (p > 0.05). The age at the start of treatment was found to be statistically significant in terms of the success of the splint (p = 0.03). Conclusions For successful treatment with Tubingen splints, the cut-off point of starting initial treatment was defined as the 15th week, with sensitivity of 84.62% and specificity of 62.50%. The success rate was 75% with a successful outcome in 78 hips. In view of these results, Graf type D, 3, and 4 dislocated hips can be successfully treated with Tubingen splints.