We undertook a prospective study comparing the unreamed interlocking nail to Hoffmann external skeletal fixation (ESF) in the treatment of 36 consecutive patients with open type IIIA and IIIB tibia fractures. The choice of interlocking nail or Hoffmann ESF was randomized, ultimately producing four different patient groups: group 1, type IIIA fractures treated by interlocking nail; group 2, type IIIA fractures treated by ESF; group 3, type IIIB fractures with interlocking nail; and group 4, type IIIB fractures with ESF. The average length of follow-up was 20.5 months. The infection rate was highest in group 3 (3 of 8). The malrotation, malunion, and nonunion rates were highest in group 4 and lowest in group 1. These results suggest the unreamed interlocking nail is a good choice for the treatment of open type IIIA tibia fractures, but not recommended for the treatment of open type IIIB tibia fractures because of the high infection rate.