OBJECTIVE Varisation distal femoral osteotomy is a well-described treatment for lateral compartment arthrosis in the young, active patient. This treatment may potentially alter the length of the lower limb . The objective of this study was to quantify the change in leg length following lateral opening wedge distal femoral osteotomy using a blade plate. METHODS Between 1998 and 2011, 29 lateral opening wedge distal femoral osteotomies were performed for symptomatic genu valgum with signs of lateral compartment arthrosis or patello-femoral symptoms. The mean age was 44.4 years (±11.3). Average follow-up was 80.2 months (±50.6). RESULTS The mean osteotomy opening was 8.3° (±2.3). The femoro-tibial mechanical axis (mFTA) was improved significantly, from 187.8° (±3.5) to 180.4° (±2.6) post-operatively (p < 0.001). The pre-operative leg length discrepancy was -0.7 cm, compared to -0.6 cm post-operatively, which was not significant (n.s.). There were five revisions to arthroplasty for disease progression at meantime of 166.6 months post-operatively. The probability of survival at 60 months was 91.4% (95% CI 74.9-100%) with end-point of revision to total knee arthroplasty and 87.6% (95% CI 74.1-100%) of revision for complications. CONCLUSIONS Lateral opening wedge distal femoral osteotomy, performed for symptomatic genu valgum, has no effect on leg length. This technique allows good correction of the axis of the lower limb; however, the complication rate is not insignificant (14%). Complications occurred mainly in post-traumatic cases and may be avoidable with attention to technique and optimum rehabilitation. The procedure should be reserved for young, active patients with significant symptoms. METHODS IV.