We investigated the biodiversity, exploitation, and conservation status of turtles in the Tonle Sap Biosphere Reserve (TSBR) of Cambodia from June 2000 through October 2001. We confirmed the occurrence or former occurrence of 4 native species of turtles (Batagur baska, Cuora amboinensis, Heosemys annandalii, and Malayemys subtrijuga) in TSBR and discuss the possible occurrence of 4 others, including 2 native species (Amyda cartilaginea and Pelochelys cantorii) and 2 exotics (Trachemys scripta and Pelodiscus sinensis). Large numbers of turtles were being unsustainably harvested from TSBR at the time of our study. Most harvested turtles were destined for urban markets in Cambodia and international wildlife markets in Vietnam and southern China, with very few kept by fishermen for household consumption. We regard any attempts to eliminate the subsistence harvest of turtles as impractical in Cambodia but recommend a complete ban on the extraction of turtles and other wildlife resources from the 3 core areas of TSBR. Incidental to our investigation of turtles in TSBR, we collected data on sexual size dimorphism and reproductive biology of M. subtrijuga. Our findings indicate that female M. subtrijuga are larger than males, and females may construct underwater nests as floodwaters begin to recede in the early dry season.