Slipped capital femoral epiphysis, the most common hip disorder in adolescence, traditionally has been classified according to symptom duration. An acute slip is 1 in which there are symptoms for < 3 weeks; for a chronic slip, there are symptoms for > 3 weeks. An acute-on-chronic slip is characterized by a combination of both with a recent exacerbation of symptoms. This classification system is misleading because it does not consider stability. A stable slipped capital femoral epiphysis has a good prognosis, but an unstable slip has a guarded prognosis. The priorities in treating an unstable (acute) slip are (1) to avoid avascular necrosis, (2) to avoid chondrolysis, (3) to prevent further slip, and (4) to correct deformity. The last priority, correcting the deformity, is associated with a high incidence of complications including avascular necrosis and chondrolysis, so manipulative reduction under anesthesia or an acute corrective osteotomy is not recommended. To address these priorities in treatment, the authors recommend preoperative bed rest to decrease the synovitis and intraarticular effusion. Operative stabilization is done in an elective fashion once the synovitis has subsided. The technique includes careful patient positioning on the fracture table, which may cause an incidental reduction, but no attempt is made to do a manipulative reduction. The technique is dependent on radiographic control. The femoral head and neck must be well visualized on the anteroposterior and lateral intensifier images before the operation is started. The slipped capital femoral epiphysis is stabilized with a single central screw, and nonweightbearing ambulation with crutches is recommended until a satisfactory painless range of motion has returned.