BACKGROUND Intramedullary nailing is commonly used for treating fractures of the tibial shaft. These fractures are one of the most common long bone fractures in adults. OBJECTIVES To assess the effects (benefits and harms) of different methods and types of intramedullary nailing for treating tibial shaft fractures in adults. SEARCH METHODS We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE and reference lists of articles to December 2009. The search was subsequently updated to September 2011 to assess the more recent literature. SELECTION CRITERIA Randomised and quasi-randomised controlled clinical studies evaluating different methods and types of intramedullary nailing for treating tibial shaft fractures in adults were included. Primary outcomes were health-related quality of life, patient-reported function and re-operation for treatment failure or complications. DATA COLLECTION AND ANALYSIS At least two review authors independently performed study selection, risk of bias assessment, and data collection and extraction. MAIN RESULTS Nine randomised and two quasi-randomised clinical trials, involving a total of 2093 participants with 2123 fractures, were included. The evidence was dominated by one large multicentre trial of 1319 participants. Both quasi-randomised trials were at high risk of selection bias. Otherwise, the trials were generally at low or unclear risk of bias. There were very few data on functional outcomes; and often incomplete data on re-operations. The trials evaluated five different comparisons of interventions: reamed versus unreamed intramedullary nailing (six trials); Ender nail versus interlocking nail (two trials); expandable nail versus interlocking nail (one trial); interlocking nail with one distal screw versus with two distal screws (one trial); and closed nailing via the transtendinous approach versus the paratendinous approach (one trial).No statistically significant differences were found between the reamed and unreamed nailing groups in 'major' re-operations (66/789 versus 72/756; risk ratio (RR) 0.88, 95% confidence interval (CI) 0.64 to 1.21; 5 trials), or in the secondary outcomes of nonunion, pain, deep infection, malunion and compartment syndrome. While inconclusive, the evidence from a subgroup analysis suggests that reamed nailing is more likely to reduce the incidence of major re-operations related to non-union in closed fractures than in open fractures. Implant failure, such as broken screws, occurred less often in the reamed nailing group (35/789 versus 79/756; RR 0.42, 95% CI 0.28 to 0.61).There was insufficient evidence established to determine the effects of interlocking nail with one distal screw versus with two distal screws, interlocking nail versus expandable nail and paratendinous approach versus transtendinous approach for treating tibial shaft fractures in adults.Ender nails when compared with an interlocking nail in two trials resulted in a higher re-operation rate (12/110 versus 3/128; RR 4.43, 95% CI 1.37 to 14.32) and more malunions. There were no statistically significant differences between the two devices in the other reported secondary outcomes of nonunion, deep infection, and implant failure.One trial found a lower re-operation rate for an expandable nail when compared with an interlocking nail (1/27 versus 9/26; RR 0.11, 95% CI 0.01 to 0.79). The differences between the two nails in the incidence of deep infection or neurological defects were not statistically significant.The trial comparing one distal screw versus two distal screws found no statistically significant difference in nonunion between the two groups. However, it found significantly more implant failures in the one distal screw group (13/22 versus 1/20; RR 11.82, 95% CI 1.70 to 82.38).One trial found no statistically significant differences in functional outcomes or anterior knee pain at three year follow-up between the transtendinous approach and the paratendinous approach for nail insertion. AUTHORS' CONCLUSIONS Overall, there is insufficient evidence to draw definitive conclusions on the best type of, or technique for, intramedullary nailing for tibial shaft fractures in adults. 'Moderate' quality evidence suggests that there is no clear difference in the rate of major re-operations and complications between reamed and unreamed intramedullary nailing. Reamed intramedullary nailing has, however, a lower incidence of implant failure than unreamed nailing. 'Low' quality evidence suggests that reamed nailing may reduce the incidence of major re-operations related to non-union in closed fractures rather than in open fractures. 'Low' quality evidence suggests that the Ender nail has poorer results in terms of re-operation and malunion than an interlocking nail.