Three patients had compartment syndrome of the leg after tibial intramedullary nailing with reaming. They were all treated successfully with emergency fasciotomy. A prospective study was done of seven additional patients who had continual monitoring of the pressure in the deep posterior compartment during tibial intramedullary nailing with reaming. In five of them, the procedure was performed three weeks or less after injury and in the remaining two, the nailing was performed later for the treatment of non-union. Two pressure peaks in the deep posterior compartment were noted: one after strong longitudinal traction was applied and the fracture was reduced and the other during intramedullary reaming. Intraoperative pressure of thirty millimeters of mercury or more were recorded in three of the seven patients. In the treatment of tibial fractures, operative procedures that involve forceful traction for a long time may predispose the patient to compartment syndrome in the leg. Close clinical observation of such patients is needed. When there is a high risk of compartment syndrome, monitoring of the pressure in the compartment may be prudent.