Over five years, 188 adult female green iguanas were captured one or more times, permanently marked, and measured at a nesting aggregation in Panama. Growth in these adult iguanas was very slow (averaging 6.8 mm/year) and appeared to be asymptotic, but there was substantial variability in the nesting female sizes observed (295 to 425 mm). This variation is biologically important because of the close relationship of female size to fecundity but little of this variation is explainable by differences in female ages (as estimated by skeletochronology) or in adult growth rates. Smaller females grew faster than larger ones but, controlling for size, younger iguanas did not grow faster than older ones. There is no evidence of alternative strategies with a trade-off between nesting sooner but smaller and nesting later but larger. Differences in adult sizes probably result from differences in juvenile growth rates, perhaps influenced by local differences in food quality and/or differences in the adult sizes at which growth trajectories asymptote. Energetic resources probably are not limiting for adult growth or reproduction. The high disappearance rate of iguanas from year to year (ca 60% per year) probably resulted mostly from mortality.