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Objective Since Helms successful bilateral cochlear implantation with good results in 1996, there have been increasing number of reports on bilateral cochlear implantation. Most second device have been implantated within one year after the first. Considering effects of long time auditory deprivation, it is not clear whether a delayed second cochlear implant serves to add additional benefits and how it may interact with central nervous system plasticity. Methods Three cases who received delayed second cochlear implants at Peoples Hospital of Peking University from 2002 to 2005 were reviewed. The interval between the first and second implants was longer than 2 years in all three patients. Sound perception, and unilateral/bilateral speech discrimination in quiet and noise were evaluated. In addition, GAP detection test was conducted in one patient. Results In one case,having both implants on provided improved performance compared to using only one implant both in quiet and noise. Presumably due to visual interference from lip-reading or short interval between second implant and testing,one patient showed no improvement from using the second implant either in quiet or noise, while the last case demonstrated additional benefits from the second implant only in quiet. In all three patients, performance in recognizing the four tones in Mandarin was superior over word recognition. Conclusions Considerable plasticity in the cerebral auditory center is preserved, despite long acoustic deprivation in some children who have received unilateral cochlear implant. Delayed second implants can result in significant improvements in some of these children. Visual interference from lip-reading may be an obstacle during retraining. The better recognition of tones in the Mandarin language may represent a different sound discrimination mechanism in the auditory system,although it may also be related to the signal processing mechanisms of the implant used (MED-EL COMBI 40+).