Adult body size is a central life history character in mosquito fitness studies. I evaluated the predictive values of pupal cephalothorax length, cephalothorax width, and wet weight for adult size (wing length) of male and female Aedes aegypti (L.) (Diptera: Culicidae). Cephalothorax length was the most consistent and accurate predictor of adult size. Width of the cephalothorax and wet weight were more variable, and they significantly decreased shortly before adult emergence. I propose that cephalothorax length could be used as a proxy for adult size to test how physical and biological factors such as resource-limited environments and competition affect mosquito fitness with the advantage that the specimen does not need to be killed.