Acoustic signals from free-ranging finless porpoises were recorded in the waters around Hong Kong during March 2000. Finless porpoises produced short-duration high-frequency clicks. Signal analysis showed finless porpoise clicks to be both “typical” phocoenid sounds, i.e. narrowband, high frequency ultrasonic pulses, and “atypical” broadband pulses with sharp onsets. Peak energy in the narrowband porpoise click spectrum occurred at 142 kHz, with negligible energy below 100 kHz. Energy was more diffuse in the spectra of broadband clicks, with a tendency towards higher frequencies. Mean pulse duration of narrowband clicks was 104 microseconds, whereas mean pulse duration of broadband clicks was 61 microseconds. Generally, finless porpoise clicks were inaudible to the human ear, except on occasion when faint, but distinct, pulses were heard from animals close to the hydrophone.