Although the intramedullary nailing is thought to be the method of choice for treatment of closed tibial shaft, there is ongoing debate on the optimal surgical approach in patients with open types of these fractures. In addition, choosing between the reamed and unreamed intramedullary nailing is still an issue for the orthopedic surgeons. In present study, we aimed to compare the outcome and consequences of OA tubular external fixation vs. unreamed intramedullary nailing in open grade IIIA-IIIB tibial shaft fractures. In a randomized clinical trial, 50 patients with open tibial shaft fractures (grades IIIA-IIIB) were recruited in Tabriz Shohada teaching centre in a 2-year period of time. They randomized in two equal groups underwent either AO tubular external fixation or unreamed intramedullary nailing. These 2 groups were matched for sex, age and fracture-grade. The follow-up time was one year. Union time, surgical outcome, postoperative complications and the ambulation time were compared between the two groups. Twenty five patients, 20 males and 5 females with a mean age of 30.80 +/- 5.24 years were allocated in unreamed intramedullary group and 25 other patients, 22 males and 3 females with a mean age of 28.92 +/- 8.88 years were studied in the external fixation group (p = 0.70 and 0.37, respectively). The two groups were matched for sex (p = 0.70) and age (p = 0.37). The time of union was 3, 4, 5 and 6 < or = weeks after operation in 28, 12, 32 and 28% of the cases in unreamed intramedullary group vs. 4, 12, 48 and 36% of the cases in external fixation group, respectively (p = 0.14). Post-operative infection, soft tissue injury, malunion and nonunion were documented in 16, 8, 0 and 4% of the cases in unreamed intramedullary group vs. 32, 12, 24 and 8% of the cases in external fixation group, respectively (p = 0.19, 0.50, 0.02 and 0.50, respectively). The mean ambulation time after operation was 2.92 +/- 2.43 weeks in the unreamed intramedullary nailing group vs. 2.68 +/- 2.14 weeks in the external fixation group (p = 0.71). Our results are in favor of unreamed intramedullary nailing against external fixation in treatment of open tibial shaft fractures.