Psychoacoustic studies of infant and toddler cochlear implant (CI) recipients could contribute to a better understanding of auditory development in this population. In this study, young CI-users' sound-detection ability was assessed using the observer-based psychophysical procedure. Detection accuracy and reaction time were examined. A stimulation method was developed to present single-electrode stimulation with concurrent ambient sound processing on other electrodes. Detection accuracy generally increased, and in some children, reaction time decreased, with increasing stimulus level. Asymptotic detection accuracy was comparable with that reported for normal-hearing children. Psychometric function slopes were comparable or shallower than those reported for adult CI users.