The Hon Chong‒Kâmpôt hills form a group of tiny karstic outcrops scattered in the alluvial plain across the southwestern border between Vietnam and Cambodia. This group hosts an exceptional concentration of endemic taxa that have been progressively discovered during the past two decades. Remarkable endemic genera of millipedes, mites, woodlice and beetles, as well as many endemic species of other arthropod groups are known from deep soil and from caves of this karst. Among them, several species remain known from only single caves or sites, despite intensive sampling. These hills are under critical threat from limestone exploitation. Most of them have already been, or are going to be, levelled during the coming years, the plan being to leave only 3 km2 of unquarried limestone in the Vietnamese part of the karst. We describe here the patterns of endemism and the patterns of threats to this karst group, and summarize the attempts that have been made so far to avoid what is turning out to be one of the worst mass extinctions of karst species documented to date.