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Chironomids have been widely used in environmental monitoring and toxicity assays. Assessment criteria for chironomids range from the molecular-biochemical level to the population level. However, the use of markers to evaluate cellular and anatomical changes in organs and systems of individuals under contaminant exposure is still incipient. In this study, we conducted a histological description of the main systems and organs of immature Chironomus columbiensis. We used fourth instar larvae, obtained from a standardized culture, and confirmed this state through morphological and molecular methods. Larvae were fixed in Duboscq solution for insects during 48 hr, dehydrated in increasing dilutions of ethanol, and embedded and mounted in historesin to obtain 3 μm sections. The digestive, nervous, excretory, and integumentary systems and the fat body and testicles were analyzed through longitudinal and transversal sections, stained with hematoxylin-eosin (HE), and further photographed and described through light microscopy. This is the first description of internal morphology performed for C. columbiensis and can help in future histopathological analysis, because through bioaccumulation some of these organs are contaminant targets. It can even be a great taxonomic tool, since the characteristics of the histological pattern of C. columbiensis presented differences compared to other descriptions made in chironomids., (© 2019 Wiley Periodicals, Inc.)