Strandings of beaked whales of the genera Ziphius and Mesoplodon have been reported to occur in conjunction with naval sonar use. Detection of the sounds from these elusive whales could reduce the risk of exposure, but descriptions of their vocalizations are at best incomplete. This paper reports quantitative characteristics of clicks from deep-diving Cuvier's beaked whales (Ziphius cavirostris) using a unique data set. Two whales in the Ligurian Sea were simultaneously tagged with sound and orientation recording tags, and the dive tracks were reconstructed allowing for derivation of the range and relative aspect between the clicking whales. At depth, the whales produced trains of regular echolocation clicks with mean interclick intervals of 0.43 s (+/- 0.09) and 0.40 s (+/- 0.07). The clicks are frequency modulated pulses with durations of approximately 200 micros and center frequencies around 42 kHz, -10 dB bandwidths of 22 kHz, and Q(3 dB) of 4. The sound beam is narrow with an estimated directionality index of more than 25 dB, source levels up to 214 dB(pp) re: 1 microPa at 1 m, and energy flux density of 164 dB re: 1 microPa2 s. As the spectral and temporal properties are different from those of nonziphiid odontocetes the potential for passive detection is enhanced.