The Siamese crocodile Crocodylus siamensis, now regarded as one of the world's most endangered crocodilians, was formerly common in the wetlands of southern Vietnam. Populations are thought to have declined in recent years, although quantitative status assessments are unavailable. We surveyed five areas previously believed to harbour the only remaining Siamese crocodile populations in Vietnam, and our results strongly suggest that viable populations are no longer extant. Crocodiles were not observed during spotlight counts of Crocodile Swamp (Nam Cat Tien National Park) or Lac Lake. Crocodiles do not occur in Upper or Lower Krong Pach Reservoirs, and these degraded sites no longer constitute suitable habitat. Remnant populations may exist in the Sere Pok River and Tay Son Lake, but these crocodiles remain subject to persecution. Population declines are attributed to a combination of hunting, habitat destruction, incidental capture in fishing nets and collecting for crocodile farms. Reintroduction to Nam Cat Tien National Park is recommended.
