Abstract Sternotherus depressus (Flattened Musk Turtle) is a threatened endemic of the Black Warrior River basin in northern Alabama. Carapace lengths taken from recaptures of turtles individually marked over an 18-year period were used to generate von Bertalanffy growth curves for both sexes. Females grew faster than males early in life and reached estimated asymptotic size at a younger age. Size-at-sexual-maturity data from previous studies indicate that males reach maturity in 1012 years, while females mature at 1215 years. Compared to a spring-dwelling Florida population of S. minor (Loggerhead Musk Turtle), the Flattened Musk Turtle has a slower growth rate, a greater age at maturity, and a smaller asymptotic size. These differing life-history characteristics likely reflect cooler water temperatures and reduced food availability in Flattened Musk Turtle habitats.