One hundred and fifty-two patients who had 154 closed fractures of the shaft of the tibia were prospectively randomized to management with interlocking intramedullary nailing either with or without reaming. Thirteen patients who had been randomized to treatment without reaming were switched to the group that had reaming because of technical reasons; these patients were excluded from the analysis of the results. An additional five patients were lost to follow-up. Thus, seventy-two patients (seventy-three fractures) who had been managed with nailing with reaming and sixty-three patients (sixty-three fractures) who had been managed with nailing without reaming were available for follow-up at an average of twelve months (range, three to thirty-three months) postoperatively. The two groups were similar with regard to demographics and the configurations of the fractures. The average total duration of the procedures performed without reaming was eleven minutes shorter than that of the procedures done with reaming (p = 0.0013). The duration of fluoroscopy was not significantly different between the two groups (p = 0.35, Mann-Whitney test). The average estimated blood loss was identical for the two groups. Seventy fractures (96 per cent) that were treated with nailing with reaming and fifty-six (89 per cent) that were treated with nailing without reaming united without the need for an additional operation (p = 0.19). Because of the small sample size, the study has insufficient power (34.7 per cent) to detect this difference if it is real. There was only one deep infection, which developed after nailing without reaming. The nail fractured after one procedure with reaming. A screw fractured after two procedures with reaming and after ten without reaming (p = 0.012); multiple screws fractured after three procedures in the latter group. Malunion occurred after three nailing procedures with reaming and after two without reaming. Four malunions were of very proximal fractures and one was of a very distal fracture. Seventeen screws and twenty-four nails were removed after nailing with reaming, and twenty screws and nineteen nails were removed after nailing without reaming; neither of these prevalences was significantly different between the two groups (p = 0.27 and 0.89; chi-square test). We concluded that there are no major advantages to nailing without reaming as compared with nailing with reaming for the treatment of closed fractures of the shaft of the tibia. There was a higher prevalence of delayed union and breakage of screws after nailing without reaming.