The biology of the endangered Tuamotu Sandpiper (Prosobonia cancellata) is essentially unknown. We analyzed vocalizations from presumed adult individuals and pairs, and family groups, recorded in French Polynesia during March 1990 and 2003. We recognized three types of vocalizations. Presumed adults uttered types I and II. These were brief (about 30–40 and 20–120 ms, respectively) and simple in structure (increasing then decreasing in frequency) but harmonically rich, with most energy in the second or third harmonics (peak fundamental frequency was about 775–1,380 Hz), as in some other Scolopacidae. Higher harmonics reached unusually high frequencies for a scolopacid (approaching 14 kHz). Call types I and II were uttered singly or as couplets, triplets, or longer sequences. Type III calls were longer (about 115–470 ms), of narrower bandwidth, and with modulations of a carrier frequency that decreased from about 1,925 to 1,305 Hz; they were given by a presumed family group and may represent calls of dependent young birds. Harmonic richness and variation in frequency and temporal variables within call types are consistent with a short range communication system.