Demographic studies on long-lived organisms are uncommon, largely because of the long time periods necessary to collect even the most basic data. We report results of the first long-term growth study of a non-Amazonian Neotropical freshwater turtle, the chelid Hydromedusa maximiliani. Differences were detected among males, females, and juveniles. Juveniles had higher growth rates (body size and mass) than adult males and females. A significant negative relationship existed between growth rate and mean body size of males and females, which was best defined by linear equations. Growth constants (k) estimated from the von Bertallanfy model were 0.094 for females and 0.073 for males, and the parameter b was 0.75 for females and 0.77 for males. Based on the von Bertallanfy equation, estimated age at sexual maturity was 14 yr (11.6–16.6 yr) for males and 9 yr (5.7–11.9 yr) for females, whereas longevity was estimated at about 100 yr for both sexes. This represents the greatest expected life span reported for a chelid turtle. Because the geographical distribution of H. maximiliani is restricted to mountainous regions of the Atlantic rain forest, one of the world's biodiversity hotspots, and because the species is long-lived and late maturing and appears to have a set of life-history traits unique among chelid turtles, a conservation program that extends beyond existing conservation units may be necessary to ensure its survival.