Understanding growth patterns is critical for determining age and size at sexual maturity and longevity in species that are severely threatened by over-collection and habitat loss, particularly in poorly understood species in tropical East Asia. Using data collected during a 9-year mark-recapture study, we fit the von Bertalanffy and logistic growth models to examine growth patterns of the endangered Big-headed Turtle (Platysternon megacephalum). Growth rate of P. megacephalum was best described by the von Bertalanffy model. Mean age at maturation for female and male P. megacephalum was 8 and 13 years. At maturity for female and male P. megacephalum, mean carapace length was 100 mm and 130 mm, respectively. We determined that counting growth rings on the carapace and plastron was not a reliable method for estimating ages. The long time to maturation in P. megacephalum may be costly in harvested populations, with individuals potentially being removed from populations prior to first reproduction. The growth patterns we have documented, and associated information on body size and age at sexual maturity, yield metrics that may be used to assess the effects of harvesting in populations and may contribute to conservation efforts for this endangered species.