We studied the determination of sex for intermediate size classes and adult sexual dimorphism in a Georgia population of Macrochelys temminckii (Alligator Snapping Turtle). We sexed turtles when possible based on size and morphometrics. We took blood samples from captured individuals and measured plasma testosterone using enzyme-linked immunoassay. We examined females and individuals for which sex was unknown using ultrasound to determine sex and reproductive status. We used testosterone concentration to confirm individual sex assignments. For all biometric measurements, adult males were larger than females. Testosterone concentrations were higher in adult and subadult males than in females. Head width did not differ between the sexes when adjusted for body size. Plastron-to-vent length (cm) and testosterone concentrations were significantly greater in adult and subadult male turtles compared to females and were valuable in determining sex of smaller adults >25 cm straight-midline carapace length.