The question of demographic decline in the Marquesas Islands is here reinvestigated through an integrated approach to the particular case of Ua Huka. We first attempt to propose a new population estimate for the period prior to European contact, thanks to an archaeologically based method that relies on the length of sleeping areas available in the housing structures recorded in the valleys. From this estimate, we then use ethnohistorical accounts to reassess local demographic evolution throughout the 19th century. This leads us to partly nuance the impact of Westerners, especially the introduction of diseases, which on Ua Huka appears to have been less critical than other factors such as sociopolitical conditions, including intense warfare, linked to unfavourable environmental conditions.