Femoral valgus osteotomy (FVO) is used as a surgery for advanced and terminal hip osteoarthritis (OA). The purpose of this study was to clarify the effect of FVO on preventing the progression of OA. The subjects were 10 patients (43.6 ± 4.6 years) who received FVO. The survey items were hip function (JOA score) and the number of patients who underwent total hip arthroplasty (THA). The causative diseases were developmental dysplasia of the hip in 7 patients, epiphyseal dysplasia 2, and pseudoarthrosis after femoral neck fracture 1. The JOA score improved from 45.4 ± 6.7 points to 60.8 ± 27.2 points at the final survey (p = 0.091). The follow-up period was 133.5 ± 32.9 months, and three joints were converted to THA (131 ± 21.7 months after osteotomy). The preoperative stages of the patients who underwent THA were advanced stages. FVO for early and advanced hip OA under the age of 50 allowed relief of symptoms and joint preservation for more than 10 years.