This study evaluated the clinical effectiveness of wireless contralateral routing of offside signals hearing aids (CROS) in patients with severe to profound unilateral sensorineural hearing loss (USNHL). Twenty-one patients with USNHL were enrolled in this prospective study. The change of subjective satisfaction was evaluated using three questionnaires (K-HHIE, K-IOI-HA, K-SSQ). Changes in objective measurements were evaluated with sound localization test (SLT) and hearing in noise test (HINT). These tests were performed at pre-CROS fitting, 2 and 4 weeks after use of CROS. Subjects were grouped according to the age: young (<40 years) vs. old (≥40 years) group. The average K-HHIE and K-SSQ scores significantly improved with the use of CROS. SLT result revealed that hit rate and error degree improved in the young group and lateralization ability improved in both groups. In quiet environments, the reception threshold for speech also indicated a significant benefit in the young group. When the noise was presented to the normal ear, HINT revealed benefit of CROS, while loss of performance with CROS use was significant when noise was presented to the impaired ear. Wireless CROS provided increased satisfaction and overall improvement of localization and hearing. Although true binaural hearing cannot be obtained, CROS is a practical option for rehabilitation of USNHL.