Anterior cruciate ligament (ACL) injury is still a challenge for the orthopaedic surgeon. The number of ACL ruptures is rising up to 61 cases per 100.000 persons/year. The estimated number of ACL injuries is around 1000 cases and the number of operated cases is 350–400 per year in Estonia. Despite long term research to find the best treatment option, we still face with problems to avoid critical mistakes during diagnosis, treatment and follow-up. There are four main problems influencing surgical outcome: tunnel positioning, arthrofibrosis, deep infection and pain. In many cases all of these problems may be present, but we mainly deal with one or two of them. Minor tunnel malpositioning does not often present a clinical challenge. If tunnel malpositioning is far from anatomic, there occur a number of complications including postoperative instability and a painful and malfunctioning knee joint. A new operation is often the only option for better outcome. However, reoperation has higher risks of rerupture, arthrofibrosis and infection. Deep infection is fortunately a less common complication affecting around 0.6–1% of operated knees. To minimize the listed complications, patient selection and critical evaluation of the surgical skills of the surgeon are crucial for successful outcome.