Traumatic ruptures of tibialis posterior tendon are much less common and consequently have received little attention. A tibialis posterior tendon rupture associated with a closed medial malleolar fracture occured in a 32 years old man due to slip down. The tendon rupture was not diagnosed before surgery but was recognized at the time of open operation. The treatment was open reduction and internal fixation at the bony fragments with primary repair of the tendon. This tendon injury, although rare, should be considered in the management of ankle fracture because the tendon rupture could easily have been overlooked and failure to recognize this at the time of injury may result in poor long - term ankle function despite a well- healed fracture.