Examination of the abdomen of the adult female and the head capsule of the mature larva indicates the grat utility of the Scanning Electron Microscope (SEM) in examining structures when searching for useful characters to deal with the taxonomy and phylogeny of gall midges (Diptera: Cecidomyiidae). Some of the structures found represent adaptations of limited value for phylogenetic considerations at higher levels. Knowlwdge about functional morphology of the ultrastructures is necessary to understand their ecological meaning and adaptive significance. SEM and ТЕМ (Transmission Electron Microscopy) examination revealed several types of integumental appendages on the female uromeres VII-X. Microtrichia, which are not innervated, nonporous sensory hairs with tactile function, and uniporous sensory hairs with both contact chemosensory (gustatory) and tactile function are present in all species. In addition, different olfactory, gustatory, and mechanosensory sensilla and additional non-innervated large spines on the superior lamella (=cercal lobe) and nonporous bristles on uromere VIII are here regarded as synapomorphies for the tribe Lasiopterini, and probably evolved partially or entirely as adaptations to the symbiosis between the midges belonging to this tribe and one or more conidiaproducing fungi. A female superior lamella largely or entirely devoid of microtrichia but with longitudinally directed ridges has probably evolved within the Dasineura complex several times. However, some of the species, which all have this type of lamella, show a short (< 600 pm) ovipositor, a tergite VIII with a pair of longitudinal rods, and are associed with fabaceous plants. These may constitute a monophyletic unit. This group includes Dasineura mariae, D. berti, D. sp. on Astragalus glycyphyllos, and D. sp. on Spartium junceum.SEM and ТЕМ examination of the head capsule of mature larva revealed in Dicerura iridis eight different kinds of sensory structures, including olfactory, gustatory, thermo- and hvgroreceptors, proprioceptors and tactile sensilla. Larvae representing different taxa and varying larval habits display a great variation concerning the ultrastructure of the headcapsule. Some characters were interpreted as adaptations to the habitat, e. G., to the life in the gall, or to predaceous or sporomycophgous life. The examinations also demostrate characters to be interpreted as synapomorphies for subfamilies, and supertribes. The phylogeny of the family was analysed, on the basis of both adult and larval characters. The reliability of the cladistic structure of the data analysed using PAUP and the support of each clade was estimated by bootstrap analyses and Bremer support. The most parsimonious trees are well supported in most of their branches. With the support of the results it is proposed here to divide the family in nine subfamilies: Catotrichinae, Lestremiinae, Micromyinae, iallactinae, Heteropezinae, Winnertzinae, Porricondylinae, and Cecidomyiinae. A key to subfamiles is included.