BACKGROUND & AIMS When performing a listening task, individuals with a hearing loss must expend greater effort to achieve the same level of comprehension as their normal hearing peers. This is particularly so in challenging listening environments, such as background noise. Little has been done to understand how the provision of a cochlear implant (CI) in patients with single sided deafness (SSD) affects listening effort. The aim of this study was to compare listening effort [using reaction time (RT)] in single-sided deafness cochlear implant (SSD-CI) users with normal hearing controls. METHODOLOGY Listening effort and target accuracy were assessed in 3 different listening conditions: monaurally using the CI alone and the normal hearing ear (NHE), free-field in quiet and free-field in noise. In all 3 conditions the participants completed an oddball paradigm consisting of odd and even numbers. RESULTS In the monaural situation, hearing through the CI resulted in significantly delayed RT compared to the NHE of SSD-CI users and controls. Further, sound presentation to the NHE in SSD-CI users demonstrated a delayed RT compared with controls. In free-field in quiet, a delayed RT was observed with the CI-On compared to the CI-Off condition, whereas in free-field in noise the opposite was observed with significantly improved RT in the CI-On condition. CONCLUSION SSD-CI users demonstrate greater listening effort than normal hearing controls in all 3 listening conditions. The NHE is dominant in quiet environments. The delayed RT with sound presentation to the NHE in SSD-CI users indicates that unilateral auditory deprivation not only impedes functional hearing in the impaired ear but also in the contralateral NHE. This is hypothesised to be due to an adverse effect on working memory for sounds and requires further research. The improvement in RT in background noise demonstrates the benefit of CI in SSD, however SSD-CI users remain at a disadvantage when compared to normal hearing controls.