OBJECTIVE: To observe the strength of thigh muscles after reconstruction of anterior cruciate ligament by autogenous bone-patellar tendon-bone graft. METHODS: Twenty-three patients, 9 males and 14 females, were followed up one year after reconstruction of the anterior cruciate ligament with autogenous bone-patellar tendon-bone graft. Through arthroscope, no intra-articular derangement was found. The strengths of isometric and isotonic contractions of the quadri ceps and the hamstrings muscles of the affected and contralateral thighs were recorded. RESULTS: The donor side for autogenous bone-patellar tendon-bone graft showed significant decrease (P lt; 0.01), but no effect on that of the hamstrings muscle(P gt; 0.05). CONCLUSION: To reconstruct the anterior cruciate ligament, harvest of the bone-patellar tendon-bone graft as a reparative material may markedly lower the strength of the quadriceps femoris muscle.