The old unreduced traumatic patellar dislocation is very rare and the results of the treatment are not always satisfactory. We report a 11 year-old boy with an unreduced patellar dislocation and a healed ipsilateral femoral fracture. The dislocation was reduced by an operative procedure. A long leg cast was applied for 6 weeks then the knee exercises were started. One year after surgery, he still has satisfactory results. This case suggests that if the dislocation is not of long duration and degenerative changes are absent in the patella and the knee joint, open reduction may be helpful in the treatment of old unreduced traumatic patellar dislocations.