Recently conventional or interlocking intramedullary nailing is being regarded as one of the most stable fixation method in the management of tibial shaft fractures. But conventional reaming technique leaves the problem of compromising the endosteal blood supply, which can be critical in the cases combined with severe soft tissue damage around the fracture site. If the endosteal blood supply can not be destroyed while affording and maintaining the same stability, it can be expected to be more favorable for the union of fracture. We analyzed 16 tibial shaft fractures managed with undersized intramedullary nailing without reaming since July 1989, the follow-up period was average 1 year and 9 months, minimum 1 year and maximum 3 and half years. The obtained results are as follows; l. In all the 16 cases, nails were inserted via closed method. Conventional Kuntscher nail was used in 3 cases, static interlocking in 7 cases and proximal dynamic interlocking in 6 cases. 2. In 15 cases, union of the fracture was achieved at from 13 to 21 weeks (average 16.5 weeks). In the other case, union was achieved at 10 months after initial IM nailing through augumentation bone graft. 3. There was no grave postop. complications such as infection, bending or rotational deformity at fracture site, metal failure of the nail or interlocking screws. 4. The fractures united without definite periosteal callus formation, which seems to be the evidence of intact endosteal circulation.