Data on body size, population density, sex ratio, age, and sexual maturity are presented for a syntopic population of Emys orbicularis and Mauremys rivulata from Cukurkoy, western Turkey. 49 E. orbicularis and 98 M. rivulata were recorded from May to October 2001. This corresponds to an estimated density of 2,250 E. orbicularis and 4,970 M. rivulata per km(2) water surface. Mean straight-line carapacial length was 124 mm for adult male (n = 13) and 146 mm for adult female E. orbicularis (n = 9); mean adult body mass was 336 g for males and 565 g for females. Average straight-line carapace length was 146 mm in adult male (n = 41) and 168 mm in adult female M. rivulata (n = 16); the mean weight was 381 g in males and 594 g in females. Sex ratios were 1.4 : 1 in E. orbicularis and 2.6 : 1 in M. rivulata (male : female). 55% of all captured E. orbicularis and 42% of all M. rivulata were juveniles. Male E. orbicularis could be sexed at 110 mm straight-line carapace length, when exhibiting 7 scute annuli (males). Equivalent data for M. rivulata were 86 mm and 3 annuli.