We conducted an intensive survey of the Vulnerable eastern hoolock gibbon Hoolock leuconedys along the west bank of the Salween River in southern China, covering all known hoolock gibbon populations in China. We found 40–43 groups, with a mean group size of 3.9, and five solitary individuals. We estimated the total population to be < 200. In the nine groups for which we recorded composition, seven comprised one adult pair and 0–3 offspring and the other two groups both comprised one adult male and two adult females. The population is severely fragmented, in 17 locations, with the largest subpopulation containing only five family groups. Compared with the population in 1985 and 1994 five subpopulations have declined and gibbons have been extirpated from nine localities, although we discovered two previously unknown subpopulations. Commercial logging, illegal hunting, agricultural encroachment and population fragmentation pose serious threats to the future of H. leuconedys in China. An integrated conservation plan, including nature reserve establishment/expansion, enforcement of existing laws, conservation education, translocation and conservation-oriented research are needed to ensure the survival of H. leuconedys in China.