The aims of the study were to analyse the change in knee laxity over time after anterior cruciate ligament (ACL) reconstruction, using either bone-patellar-tendon-bone (BPTB) or hamstring (HS) tendon autografts, and to compare the knee laxity measurements between the study groups both pre-operatively and on multiple follow-up occasions. Another aim was to compare the radiographic findings in terms of degenerative changes between the study groups. A randomised series of 71 patients, who underwent ACL reconstruction using BPTB or HS tendon autografts and interference screw fixation, were included in the study. Of these patients, 47/71 (66%) attended a clinical examination, including laxity measurements using the KT-1000 arthrometer, pre-operatively and on four post-operative occasions; 6 months, 1 year, 2 years and 7 years after the reconstruction. The BPTB group consisted of 22 patients, while there were 25 patients in the HS group. There were no significant differences in the mean side-to-side knee laxity between the BPTB and the HS group pre-operatively or at the follow-up examinations. There was a tendency towards a reduction in side-to-side knee laxity over time in both groups, measured with the KT-1000 arthrometer. The decrease was significant when analysing the injured and uninjured knee separately (injured side p < 0.001 (BPTB) and p = 0.005 (HS), uninjured side p = 0.008 and p = 0.042, respectively). Forty-four patients (BPTB 21, ST 23) underwent a radiographic assessment at the 7-year follow-up, which revealed no significant differences between the study groups in terms of osteoarthritic findings classified according to the Fairbank and Ahlbäck rating systems. In overall terms, osteoarthritis was identified in 16% (BPTB 19%; ST 13%; n.s.) according to the Ahlbäck rating system and 68% (BPTB 67%; ST 70%; n.s.) according to the Fairbank rating system. There were no significant differences in knee laxity measurements between the two study groups pre-operatively or at 7 years. A decrease in knee laxity over time was seen in both groups. There were no significant differences between the BPTB and ST groups in terms of osteoarthritic findings at 7 years.