Long-term outcomes of early implanted, young adult cochlear implant (CI) users remain variable. We measured auditory discrimination by means of event-related potentials in this population to examine whether variability at the level of cortical auditory processing helps to explain speech abilities. Using an auditory oddball paradigm, the P300 and Mismatch Negativity (MMN) were measured in eight young adult CI users and fourteen normal-hearing peers. We related P300 amplitude and latency to clinical speech perception scores in quiet and to duration of deafness. All individuals showed P300 responses. The MMN response was less robust in both groups. There was no evidence for differences in P300 responses between CI users and controls. P300 amplitude was associated with speech perception scores (r = .70, p = .05) and duration of deafness (r= -.83, p = .009). Early CI implantation yields good auditory processing outcomes at young adult age and, in contrast to MMN, the P300 provides a robust measure for auditory processing on an individual level. At the cortical level, early implanted, long-term CI users have good auditory discrimination, leaving variability in implantation outcomes unexplained. This group shows unique insight into the long-term neurophysiological underpinnings of early implantation.