Two patients had displaced femoral neck fractures at the bone-screw interface after in situ fixation of slipped capital femoral epiphysis. Both fractures required closed reduction and internal fixation. Inadvertent derotation of the femur occurred in both patients and allowed fixation of the fracture through the intramedullary canal of the femoral neck without anterior penetration of the pins into the joint; a nonunion occurred in this patient. The other patient developed chondrolysis and avascular necrosis. Because the femoral neck is vulnerable to stress fractures in young adults, there is some question whether pins placed anteriorly through the femoral neck cortex should be removed.