['To determine whether packing of the cochleostomy site influences electrically evoked compound action potential (ECAP) thresholds.', 'Prospective nonrandomized control study.', 'Tertiary referral pediatric hospital.', 'Eleven consecutive children who received unilateral or bilateral cochlear implants (16 Nucleus 24RE Freedom precurved advanced off-stylet electrode arrays [Cochlear Corp., Lane Cove, New South Wales, Australia]) between June and September 2008.', 'Electrically evoked compound action potential thresholds were evoked by stimulation of basal (electrode 3), mid (electrode 9), and apical (electrode 20) electrodes during cochlear implant surgery in the operating room. The first recording was completed immediately after insertion of the electrode array before cochleostomy packing, and the same measures were collected immediately after the packing. The time between recordings was 5 minutes.', 'Electrically evoked compound action potential thresholds evoked by the apical electrode did not significantly change from pre- to post-cochleostomy packing, but ECAP thresholds increased significantly after packing when evoked by the mid-array electrode (mean, +10 clinical units; p < 0.001) and decreased significantly when evoked by the basal electrode (mean, -5.6 clinical units; p = 0.023). These changes were unrelated to passive changes occurring over the first 5 minutes after insertion of the electrode array.'] Does packing of the cochleostomy site affect auditory nerve response thresholds in precurved off-stylet cochlear implants?