ABSTRACT Background: Blount disease is a developmental disorder affecting the posteromedial part of the upper tibial growth plate resulting in complex knee deformity. Surgical correction of such deformity is challenging for orthopaedic surgeons. The goal of this study was to evaluate the results of gradual deformity correction of delayed-onset Blount disease using the Ilizarov device. Methods: Sixteen knees in 13 patients with delayed-onset Blount disease were operated for gradual deformity correction using the Ilizarov fixator at Zagazig University Hospital between June 2013 and May 2017. Clinical (tibial torsion, shortening, and range of knee motion) and radiographic parameters (tibiofemoral angle, mechanical axis deviation, and medial proximal tibial angle) were used for evaluation. A P-value of <0.05 was statistically significant. Results: The mean follow-up period was 24.4 ± 7.1mo. All patients were satisfied with the final range of knee motion, with a mean of 125 ± 8.1 degrees of flexion. Internal tibial torsion and limblength discrepancy were significantly improved at the end of the follow-up. There was a statistically significant difference between the preoperative and the final mean of the radiographic measurements. Nine patients had pin track infection, and one patient had common peroneal nerve neurapraxia that completely resolved. Conclusions: Gradual deformity correction of delayed onset Blount disease using the Ilizarov device had satisfactory clinical and radiographic outcomes with a low incidence of serious surgical complications. Key Words blount, late onset, ilizarov, gradual correction