Mentawai gibbons (Hylobates klossii) are one of the nine species of gibbon in Indonesia, all of which are threatened with extinction. We present a view of the future for gibbons on the Mentawai Islands using information from previous research as well as recent surveys. The largest gibbon population and habitat is currently in the Siberut National Park area, with approximately 10,484 individuals. In addition, there are 13 locations outside the national park with densities ranging from 1.04 groups/km2 to 4.01 groups/km2. A serious threat to the Mentawai gibbon is forest loss and hunting. Our survey also shows that the cultural value of Mentawai gibbons is being lost due to acculturation with modern culture. Uma (the Mentawai longhouse) and sikerei (the Mentawai shaman) are cultural symbols that are no longer found on the islands of Sipora and North and South Pagai. Currently there are only 94 uma and 135 sikerei (who have an average age of 64 years) on Siberut Island. We recommend conservation activities at the grassroots level for the Mentawai gibbon, activities that encourage local community capacity development and enhance the local economy, whilst at the same time strengthening Mentawai cultural and customary values.