In North America, in situ pinning is the most common treatment for a stable slipped capital femoral epiphysis (SCFE), with generally good results and relatively low risk of avascular necrosis. Since the recognition that even a mild SCFE can cause femoroacetabular impingement, there has been a reconsideration of the goals of treatment, particularly for moderate, severe, or unstable slips. The modified Dunn approach for moderate or severe SCFE involves a surgical hip dislocation, creation of a retinacular flap, controlled open reduction of the epiphysis, and internal fixation of the slip. It has the advantage of correcting the pathoanatomy at the site of the deformity and at the time of diagnosis, minimizing secondary chondrolabral damage. The short-term results are generally good to excellent with few complications. The modified Dunn technique is, however, technically complex and more invasive than in situ pinning, with some inherent risk of avascular necrosis because of the proximity to the lateral retinacular vessels. When performed by experienced surgeons, the modified Dunn technique is an ideal technique for the treatment of moderate to severe SCFE. Because of the technically challenging nature of the procedure, it is recommended that it be performed in tertiary care centers by surgeons with experience in this technique.