A statistical analysis of several morphometric variables of the freshwater shrimp Potimiirim mexicana, which has been described as a sequential protandrous hermaphrodite, is presented. The purpose of the study is to test, statistically, that organisms can be classified by sex, analyzing their size and other morphological variables. A total of 191 organisms were collected in the Máquinas River, Veracruz, Mexico. The technique used was that of classification trees, through which will likely determines the significant variables in the variable "response", as well as those required for discrimination. This technique corroborated the theory that the total length of the body is necessary for discrimination of the sex variable, but also brought the result that, statistically, two more variables are important in this discriminatory process, the length of the second pleopod and length of the carpus of the third pereiopod. The technique resulted in a correct classification of 82% using the three variables. What is significant is that the process generating the classification tree shown, in a simple and practical manneer, the variables necessary for this process and their individual discriminatory power.