In this study morphological characteristics of Neochetina eichhorniae (Warner, 1970) are described and illustrated. This species has been used for the Biological Control of waterhyacinth (Eichhornia crassipes (Mart.) Solms-Laubach, 1883). In the egg, the changing appearance of the chorion is given by the embryonic development. Description of larval head capsule chaetotaxy was done. Three larval instars were identified by measuring the head capsule width; microsculpture of the body larva was studied, microspines were evident with different arrangements in thorax and abdomen, two types of spiracles were found; the more distinctive was the dorsal spiracle in the abdomen, which is sclerotized, with sensory organs at its apex. The external morphology of N. eichorniae adult is very similar in both sexes, the main difference among them is the rostrum. Description of the wings, proventriculus and genitalia, important structures in the taxonomy, is provided. The morphological characteristics of N. eichhorniae found in this study can be use to separate from N. bruchi (Hustache) which has been released in many countries. This is the first morphological study of N. eichhorniae in Mexico.
