Cochlear implantation is often performed on one side while the other side is provided with a conventional hearing aid (HA). For these subjects bimodal hearing (HA on one side and cochlear implant (CI) on the other side) is often the provision of choice. The aim of our study was to describe the benefit in terms of speech perception in quiet and in noise for a large group of bimodal listeners. Secondly, we aimed to investigate the influence of hearing thresholds on the HA side on bimodal hearing. Sentence recognition with hearing aid alone, cochlear implant alone and bimodally were assessed in 148 experienced adult CI listeners. Data were analyzed for bimodal summation using measures of speech perception in quiet and in noise. Most of the subjects showed improved sentence recognition in quiet and in noise in the bimodal condition compared to the hearing aid-only or cochlear implant-only mode. The large variability of bimodal benefit in quiet can be partially explained by the degree of pure tone loss on the HA side. Also, subjects with better hearing on the acoustic side experience significant benefit from the additional electrical input. Bimodal summation shows different characteristics in quiet and noise. Bimodal benefit in quiet depends on hearing thresholds at higher frequencies as well as in the lower- and mid-frequency ranges. No correlation with hearing threshold in any frequency range was observed for bimodal benefit in noise.