This study examined the benefits and possible risks of immediate continuous passive motion after autogenous patellar tendon reconstruction of the anterior cruciate ligament. Thirty patients scheduled to undergo ACL reconstruction were prospectively randomized into two groups, CPM and non-CPM. Postoperatively, those in the non-CPM group wore a hinged knee brace. Those in the CPM group were kept on a CPM machine 16 hrs a day while in the hospital and they used it 6 hrs a day for the first 2 weeks postoperatively. After surgery the patients were assessed for hemovac drainage, range of motion, swelling, effusion, subjective pain, and use of pain medication. The CPM group had significantly less swelling and effusion, required less pain medication, and had greater knee flexion. No differences were found in hemovac drainage, passive knee extension, or subjective pain reports despite a significantly greater use of pain medication in the non-CPM group. The results suggest that immediate CPM after ACL reconstruction is safe and facilitates early range of motion by decreasing the amount of pain medication, effusion, and soft tissue swelling.