Transcranial routing of signal (TCROS) was accomplished using completely-in-the-canal (CIC) hearing aids in 5 profoundly unilaterally hearing-impaired individuals. The functional gain realized by the participants far exceeded the gain predicted by measuring the acoustic output and real ear aided response of the hearing aids. The difference between predicted and functional gain increased with signal frequency and was attributed at least in part to mechanical vibration of the hearing aid in the external canal. Implications for fitting unilateral hearing loss using TCROS amplifying systems are discussed.