When programming a Cochlear® device, two measurements are normally assessed. T levels relate to the quietest sound the CI user can hear i.e. thresholds, and C levels are comfortable levels which are tolerable for the CI user. If these levels are incorrectly set then quiet sounds may not be heard well or may be heard too loudly (T levels incorrectly set) or sound may be loud and uncomfortable (C level incorrectly set). Some studies have shown that having T levels set a little higher gives better speech and auditory thresholds, while others show a detrimental effect. In this study, 15 experienced Cochlear® adult users were given four different programmes. Programme 1, T and C levels were set to measured levels; Programme 2, C level only was reduced below measured level; Programme 3, T levels were below measured levels; and Programme 4, T levels above measured levels. Performance was then measured on auditory thresholds, sentence recognition and monosyllabic words for each programme. Unsurprisingly auditory thresholds were better when T levels were higher, but this did not transfer to better speech recognition and word scores. Best performance occurred when the original map was used. Poorest performance occurred for the reduction in C level with poorer scores on auditory thresholds, sentence recognition in quiet, and word recognition in quiet and noise. Therefore, the study illustrates the importance of measuring C levels correctly as this can impact on performance. The lack of findings with the T levels, could be because the T levels were not adjusted enough to affect performance in the test conditions, and these should still be measured as accurately as possible. This provides a challenge to paediatric audiologists as it can be difficult measuring these levels in children who have never heard before.