The management of clients presenting with “unaidable” unilateral hearing loss is a challenging task that hearing healthcare professionals frequently confront. One method commonly chosen to address this issue is a CROS (contralateral routing of signals) or BiCROS (bilateral CROS) hearing instrument fitting. Both CROS and BiCROS fittings attempt to overcome the adverse effects of the head shadow effect by providing awareness of sound from all directions around an individual, even if sound originates from the side of an ear with little or no usable hearing. This goal is achieved by positioning a microphone over the unaidable ear that transfers all sound via wires or radio frequency (RF) transmission to a receiver located at the better hearing ear. As with any hearing instrument technology, it is important to evaluate the functionality of the CROS/BiCROS system and, if required, perform adjustments to meet the unique auditory needs of the individual being fitted. Probe-microphone measurements represent an invaluable tool for achieving these goals. These measurements can be used to inform clients about the impact of the head shadow effect and to demonstrate how the selection of CROS/BiCROS technology can overcome it. Furthermore, probe-microphone measurements represent an ideal method of ensuring that CROS/BiCROS hearing instruments are fitted and functioning appropriately so as to maximize the potential benefit to the wearer. Given the unique manner in which these devices function, it should come as no surprise that the fitting and verification protocols used with CROS/BiCROS hearing instruments vary somewhat from those used with the typical hearing instrument. This article will discuss a number of issues and techniques that should be considered when fitting and verifying CROS/BiCROS hearing instruments using probe-microphone systems. CANDIDACY AND IMPLEMENTATION