Patellar tendon ruptures are relatively rare. The rupture may be caused by direct trauma, but is mostly caused by acute or chronic excessive traction force. Degenerative bone/tendon disease may also give rise to rupture. The diagnosis, which usually is not difficult to make, may easily be overlooked when active extension is still possible as may happen in case of a rupture due to an avulsion fracture at the tendon-bone junction. Impaired extension makes operative treatment necessary. Long term follow-up results show excellent function following early repair.