For endangered species management a shared understanding of the different beliefs, opinions and factual knowledge that local people hold towards the target species is imperative. To take these views into account, detailed assessments need to be made of how they differ between individuals, and, crucially, what beliefs and views are shared. These assessments require an ethnozoological approach, using tools from both the natural and the social sciences. Here we focus on the beliefs, opinions and knowledge about Javan slow lorises Nycticebus javanicus in 12 Sundanese communities of West Java, Indonesia. Javan slow lorises are small, nocturnal, venomous primates that are threatened by habitat loss and over-exploitation for the illegal pet trade. Based on detailed interviews with 79 informants from June 2011 to June 2013, and using cluster and cultural domain analyses, we identify and document 5 different topics, i.e. trade and exploitation, taboos against disturbing or capturing, venomous primates, blood myths and mystical powers. The most salient topics were factual (activity pattern, habitat use) or related to the taboo on collecting or disturbing slow lorises. In communities with strong traditions, taboos and beliefs in place, slow lorises were found in seemingly unlikely habitats, in or adjacent to the villages; where these beliefs were absent, slow lorises were less known to the communities, and the slow lorises were either less abundant or extirpated. We conclude that it is imperative that any conservation programme implemented in West Java, be it management, mitigation, or education, must take into account the traditions, beliefs and taboos regarding slow lorises.