PURPOSE: An observation was made by the senior author of this paper that patients reported changes in their hip function after a medial opening wedge high tibial osteotomy (MOHTO) for varus pattern osteoarthritis. Alignment changes at the hip after MOHTO have not been previously documented. This study assesses coronal alignment changes at the hip after MOHTO. METHODS: We retrospectively analysed pre- and post-operative lower limb alignment radiographs of patients who underwent MOHTO. The medial proximal tibial angle (MPTA) and mechanical axis deviation (MAD) were measured to assess the alignment changes created by the MOHTO. The coronal alignment changes at the hip were evaluated using the mechanical greater trochanter angle (MGTA). RESULTS: 29 osteotomies in 27 patients were included in this study. Results showed MOHTO created alignment changes at the hip. A positive correlation was found between the size of the correction at the knee and the subsequent changes at the hip. The change in the MGTA had a stronger correlation with the MAD than with the change in MPTA (r = 0.684 vs. 0.585). It was found that age, weight, height and BMI had no significant influence on these correlations. CONCLUSIONS: Increased correction by the MOHTO lead to increased change in the coronal alignment of the hip. These changes are likely to result in an alteration in the weight bearing portion of the femoral head and the function of the abductors and we recommend assessing the hip joint as part of pre-operative planning. LEVEL OF EVIDENCE: Prognostic level IV.