Various materials are used to fill osteotomy defects created in the medial opening wedge high tibial osteotomy (MOWHTO). Our hypothesis was that a bone allograft would provide the osteotomy site bone healing within the expected time. We performed the MOWHTO using a cancellous bone allograft in 310 knees in 284 patients between 2000 and 2005. Internal fixation was achieved with a T-profile AO plate. Preoperative and postoperative radiographic measurements were taken and statistically processed. All patients were followed up for a period ranging from three to eight years, or 5.9 years on average. Implanted cancellous bone allografts <or=9 mm healed within 12 weeks in 90% of cases. With the properly selected patient and surgical technique, use of a cancellous bone allograft in MOWHTO represents a satisfactory choice in providing bone healing.