This study documented postoperative morbidity during the first 4 months following anterior cruciate ligament (ACL) reconstruction using either patellar tendon or hamstring tendon autograft. Sixty-five patients undergoing primary arthroscopically assisted single-incision ACL reconstruction were randomized to have a central third bone patellar tendon bone autograft (PT) or a doubled semitendinosus/doubled gracilis autograft (HS). Postoperatively patients undertook a standard 'accelerated' rehabilitation protocol. Patients were reviewed after 2 weeks, 8 weeks, and 4 months. At each review the location and severity of general knee pain and the presence and severity of anterior knee pain (AKP) were recorded as were the presence and size of an effusion as well as the active and passive flexion and passive extension deficits compared to the contralateral limb. Pain on kneeling, KT-1000 measured side to side difference in anterior tibial displacement, isokinetic assessment of quadriceps and hamstring peak torque deficits, IKDC score and Cincinnati sports activity level were also recorded after 4 months. After 2 weeks more patients in the PT group complained of AKP and reported that the pain was more severe. After 8 weeks there was no significant difference between the groups for any variable. After 4 months the severity of general pain experienced and the incidence of pain on kneeling were greater in the PT group. The PT group also demonstrated a significantly greater quadriceps peak torque deficit at 240 degrees /s. IKDC scores were higher in the HS group, but Cincinnati sports activity scores were higher in the PT group. Although we observed a lower morbidity in the HS group, primarily related to pain, the severity of pain in both groups was relatively low and, in light of the higher mean sports activity level observed in the PT group at 4 months the clinical impact of the difference may not be significant.