External fixation is regarded as the treatment of choice for type 2 and 3 open tibial fractures. However, external fixation alone, especially of an unstable fracture, can be complicated by high incidence of malunion, delayed union, loss of reduction, refracture, and pin-tract infection. Some surgeons tried to treat such problems by secondary intramedullary nailing, but they came to different results. The purpose of the present study is to eveluate our experience with secondary intramedullary nailing after external fixation of 6 cases of type 3B open tibia fractures and 1 case of type 3B femur fracture. These cases were followed for more than 13 months and the following results were obtained. 1. The external fixation had been maintained for an average of 62 days. 2. The mean interval between removal of the external fixator and intramedullary nailing was 23 days. 3. Antibiotics was injected for 2 weeks after removal of external fixator. 4. Reamed intramedullary nailing with static interlocking were done in all 13 cases. 5. Deep infections developed in 2 cases, one case which had been pin-tract infection was around intramedullary nail and the other in fracture site. 6. All cases were healed ultimately and average union time after nailing was 9 months.