Existing clinical studies have not proven which graft is to be preferred in anterior cruciate ligament (ACL) reconstruction. In recent years, bone-patellar tendon-bone and hamstring tendons have been the most frequently used graft types. Muscle strength deficit is one of the consequences after ACL reconstruction. The aim of this study was to evaluate possible differences in hamstring and quadriceps muscle strength and knee function 5 years after ACL reconstruction between the BPTB and the STG groups. The study group consisted of 288 patients (132 women, 156 men) with a unilateral ACL rupture who had received a BPTB (175 patients) or STG (113 patients) ACL reconstruction. Lower extremity concentric isokinetic peak extension and flexion torques were assessed at the angular velocities of 60 degrees /s and 180 degrees /s. The International Knee Documentation Committee (IKDC), the Tegner activity level, the Lysholm knee and the Kujala patellofemoral scores were also collected. Isokinetic quadriceps peak torque (percentage of the contralateral side) was 3.9% higher in the STG group than in the BPTB group at the velocity of 60 degrees /s and 3.2% higher at the velocity of 180 degrees /s and the isokinetic hamstring peak torque 2% higher in the BPTB group than in the STG group at the velocity of 60 degrees /s and 2.5% higher at the velocity of 180 degrees /s. In both groups the subjects had weaker quadriceps and hamstring muscle strength in the injured extremity compared with the uninjured one. In the single-leg hop test (according to the IKDC recommendations) there was a statistically significant difference (P = 0.040) between the groups. In the STG group, 68% of the patients had the single-leg hop ratio (injured vs. uninjured extremity) > or =90%, 31% of the patients 75-89% and 1% of the patients <75%, while in the BPTB group the corresponding percentages were 72, 21 and 7%. However, no statistically significant differences in clinical outcome were found between the groups as determined by the IKDC, Tegner activity level, Lysholm knee and Kujala patellofemoral scores.