Slipped capital femoral epiphysis is usually treated with in situ fixation to prevent progression of deformity. However, slipped capital femoral epiphysis always is associated with structural risk factors for hip dysfunction in addition to the risk of slip progression. Femoro-acetabular impingement causes some mechanical abnormality in every hip affected by slipped capital femoral epiphysis, even when the slip is mild. The severity of femoro-acetabular impingement caused by slipped capital femoral epiphysis depends on several factors. Cumulative injury to the articular cartilage can result from impingement, and it is better to prevent this type of injury than to treat it later. In situ fixation alone rarely relieves femoro-acetabular impingement in slipped capital femoral epiphysis. Skillful and precise in situ fixation allows careful analysis of hip function in the stabilized slip by eliminating the major risk of acute instability. The more subtle risk of long-term articular damage caused by femoro-acetabular impingement must be considered. The treatment of femoro-acetabular impingement in patients who have slipped capital femoral epiphysis is a separate issue from instability of the proximal femoral physis. Femoro-acetabular impingement must be assessed in every hip that is affected by slipped capital femoral epiphysis, even when the deformity is mild. Several treatment options exist for treating femoro-acetabular impingement associated with slipped capital femoral epiphysis.