After reconstruction of the anterior cruciate ligament (ACL) afferent proprioceptive information from the knee joint may be altered. In order to examine changes in central activation patterns, spectral features of the electroencephalography (EEG) were measured. Patients after ACL reconstruction and healthy controls carried out an knee-angle reproduction task in a groups x limbs x trials design. Cortical activity was recorded using international standards. FFT were conducted to determine power at Theta, Alpha-1, Alpha-2 and Beta-1. Statistics show significantly larger aberrations in the reconstructed limbs compared with the controls whereas there are no differences between the uninvolved land controls. Brain activity demonstrates significantly higher frontal Theta-power (F3, F4, F8) in both limbs of the ACL group vs the controls and a significantly higher Alpha-2 power was shown in the ACL-reconstructed limb compared with controls at parietal positions (P3, P4). No such differences were found between the uninvolved side and the controls. The EEG was able to measure a change in joint position sense at the cortical level after the reconstruction of the ACL. The results of these findings might indicate differences in focused attention with involvement of the anterior cingulate cortex (frontal Theta) and sensory processing in the parietal somatosensory cortex (Alpha-2).