Sometimes, total knee replacement (TKR) is performed after a tibial osteotomy. It is not known if the osteotomy influences the clinical process of a TKR. The aim of this study was to look at the clinical outcome of a TKR after high tibial osteotomy (HTO) compared to a TKR with no HTO. Between 1995 and 2005, 41 post-HTO TKRs (group A) with a minimum follow-up of ten years were selected. In parallel, it was selected a control group undergoing simple TKR, consisting of 41 patients (group B) matched with group A. The Knee Society Knee Score (KS), Knee Score Functional Score (FS), the Oxford Knee Score (OKS), and the range of motion (ROM) were used for evaluation at one, five and ten years after surgery. The Insall-Salvatti ratio (ISR), the posterior tibial slope (PTS), and the joint height line (JHL) were also measured both pre-operatively and post-operatively. No differences were found between both groups in KS, FS, OKS, and ROM at the pre-operative stage or at any of the post-operative controls. Higher patellar height was found in group A, both pre-operatively and post-operatively (p < 0.005), and the same for PTS pre-operative (p < 0.001) and post-operative (p < 0.05). No differences were found regarding the JHL. Post-operative differences were found among the post-HTO subgroups at the FS (p < 0.02), the OKS (p < 0.05), and the ROM (p < 0.01) as a function of whether there was a varus or a valgus deformity before the TKR. A HTO was not determinant for having a worse outcome at the TKR, even when there were radiographic differences. The coronal alignment with valgus deformity pre-TKR after a HTO showed better functional results than in the case of varus deformity. Level of evidence III.