Аннотация:Miniaturization can strongly aff ect the structure of insects, and both common and unique features have been found in diff erent groups. However, there have been no previous studies focused on the anatomy of miniature Brachycera. In this work, the internal structure of the adults of two miniature Brachycera, Leptocera sp. (Diptera, Sphaeroceridae) and Hydrellia albilabris (Meigen, 1830) (Diptera, Ephydridae) was studied for the first time using series of histological sections and computerized 3D reconstructions. Despite the small size of these miniature flies, all their organ systems retain a complex level of organization characteristic of larger representatives of related taxa.Even the tracheal system shows no essential simplifi cation, even though it was revealed earlier in most miniature insects. A comparative analysis of changes in the relative volumes of organ systems has been carried out. The generaltrends of organ allometry identifi ed earlier have been shown to be also valid for miniature Diptera; however, the reproductive systems of Leptocera sp. and Hydrellia albilabris occupy a much smaller relative volume than that of miniature insects from other orders.