Recently published papers implicate a genetic predisposition towards tendon and ligament injury. Studies have shown that COL1A1 Sp1 binding site polymorphism was implicated in ACL ruptures, however findings for tendon ruptures are inconclusive. ACL reconstruction is performed using autologous grafting of gracilis and semitendinosus tendons. This study was conducted on patients operated by a single surgeon in University Hospital „Sveti Duh” from June 2007 until June 2012. A retrospective analysis of the operated patients was performed and a group of patients with graft ruptures was identified. We excluded from the sample those patients that suffered a reeinjury in the early postoperative period of up to one year after the surgery. This was done in order to exclude the possible influence of technical errors during surgery and rehabilitation protocol errors on graft injury. The control group of patients consisted of injured patents at least one year after surgery that returned to their preoperative level of activity. The genetic polymorphism of the Sp1 binding site of the COL1A1 gene was assessed in the DNA extracted from peripheral leukocytes of the two groups. After statistically interpreting the results of the DNA analysis our conclusion is that the presence of Thimine (T) on Sp1 binding site of COL1A1 gene increases the risk for tendon injury in patients operated for ACL rupture. Furthermore, the statistical analysis performed also identified younger age as a risk factor for tendon injury.