Little is known about underwater hearing abilities of diving birds. To help fill this gap we measured audiograms of cormorants (Phalacrocorax carbo) using two different methods. Wild-caught cormorant fledglings were anesthetized and their auditory brainstem responses (ABR) to clicks and tone bursts were measured; first in an anechoic box in air and then in a large water-filled tank with their head and neck submerged. In addition, audiograms were obtained from two adult cormorants using the psychophysical method of constant stimuli both in air and underwater. The shape of audiograms obtained from in-air ABR-recordings was similar to that reported for birds of similar size. The highest sensitivity in air was found at about 2 kHz, while the most sensitive response was at about 1 kHz underwater. In general, the audiograms obtained from psychophysical measurements were similar to the ABR audiograms but had much higher sensitivity than the ABR audiograms. The results from both methods suggest that cormorants have rather poor in-air hearing compared to similar-sized birds. Their underwater hearing sensitivity, however, is higher than what would have been expected for purely air-adapted ears, and it is likely that cormorants use their underwater hearing abilities during foraging dives.