In the upper Gulf of California, a lucrative fishery of the Cortes geoduck Panopea globosa (Dall 1898) is developing rapidly. Both exploited and unexploited areas for this fishery still exist in this area. The effect of the data source of the length-atage data on growth models fitted to Panopea globosa was evaluated. Five growth models were tested: von Bertalanffy, logistic, Gompertz, Schnute, and Schnute-Richards. The parameters of each model and their confidence intervals (CIs) were computed using the maximum likelihood method. Multimodel inference was used to average the asymptotic length for each area. The bestfitting model was selected using Akaike's information criterion (AIC). According to this criterion, the logistic growth model best described the growth of P. globosa in unexploited beds, and the Schnute models performed best in exploited beds. The asymptotic length values obtained frommultimodel inferencewere 161.88 mm (95% CI, 161.83–161.93 mm) in unexploited beds and 205.20 mm (95% CI, 197.60–212.96 mm) in exploited beds. The latter value is the largest asymptotic length obtained for any Panopea species worldwide. In conclusion, the data source of the length-at-age data clearly affects the performance of growth models.