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Increased femoral anteversion can be associated with hip instability, redislocation after closed reduction, and subsequent early degenerative arthritis. Our study compared proximal femoral anteversion of affected and unaffected sides of patients with unilateral developmental dysplasia of the hip (DDH) on two-dimensional computed tomography. The primary aim was to evaluate whether femoral anteversion at the time of treatment affected the outcome of patients with unilateral DDH treated by closed reduction.A retrospective review of 89 patients (82 females; 53 left; mean age: 26.6 months) with unilateral DDH was performed. Anteversion angle (AA) of the femur and acetabular index (AI) of both affected (AAa; AIa) and unaffected (AAu; AIu) hips were measured on two-dimensional CT scan performed no more than seven days prior to the index surgical procedure.Among the 89 patients, 50 underwent closed reduction (56.2%), 38 underwent open reduction with or without pelvic osteotomy (42.7%), and one patient refused treatment (1.1%). Overall, the mean AAa was 28.1° ± 10.2° (range: 6.3°-54°) and mean AAu was 25.2° ± 9.9° (range: 1.9°-52.5°) (t = 3.2, p = 0.002). Tönnis type 2 hips did not show any statistically significant difference between AAa and AAu (p = 0.386), while Tönnis types 3 and 4 hips had significantly higher AAa than did AAu (t = 3.7, p = 0.001). There were significant correlations between age and AAa (coefficient = 0.4; p 0.001) and AAu (coefficient = 0.304; p = 0.004). Correlation analysis showed that AIa did not improve with age in any Tönnis group (r: - 0.24, p = 0.823; F = 0.039, p = 0.962). AAa, AIa, AAD, AID, and Tönnis grade distribution were similar in patients with good (no redislocation) and poor outcomes (redislocation) (p 0.05).In patients with unilateral DDH, anteversion angle (AA) was found to be significantly different between affected and unaffected sides. However, the difference had very limited or no clinical significance, as redislocation/sub-luxation was not influenced by AA values.