Semi-dry grasslands are of high nature conservation interest both at national and European scales due to their high biodiversity and species richness. For effective conservation, however, the variation in floristic composition and distribution of these grasslands need first to be described. In Hungary, there is currently no comprehensive survey and classification of semi-dry grasslands. Therefore, the aim of this study was to (i) describe the variation in species composition of Hungarian semi-dry grasslands by a country-scale cluster analysis based on a large database; (ii) describe the types (clusters) and compare these descriptions with those in the phytosociological literature, and finally (iii) formulate a new syntaxonomical system for Hungarian semi-dry grasslands. For this analysis 699 relevés were selected in which the percentage cover of at least one of the grasses Brachypodium pinnatum, Bromus erectus, Danthonia alpina, Avenula adsurgens, A. pubescens or A. compressa reached >10%. A geographical stratification of the dataset was performed and then it was split randomly into two equal parts (training and test datasets). Following outlier exclusion and noise elimination, clustering was performed separately for both datasets. The optimal number of clusters was determined by validation. The number of valid clusters was the highest at the level of ten clusters, where seven clusters appeared to be valid. The valid clusters are separated geographically; however, there are considerable overlaps in the species compositions. According to our results, all the grasslands belong to the Cirsio-Brachypodion alliance. The seven valid clusters are assigned to five main groups of semi-dry grasslands in Hungary: 1. Brachypodium pinnatum (and partly Bromus erectus) dominated, species rich meadow-steppe-like grasslands occurring on deep loess in central Pannonia, identified as Euphorbio pannonicae-Brachypodietum Horváth 2009; 2. Brachypodium pinnatum dominated mountain grasslands restricted to the Bükk Mountains; identified as Polygalo majoris-Brachypodietum Wagner 1941; 3. mostly Bromus erectus dominated grasslands on shallow, calcium/rich soils of the Dunántúl region, proposed as a new association Sanguisorbo minoris-Brometum erecti Illyés, Bauer & Botta-Dukát 2009; 4. Brachypodium pinnatum and Danthonia alpina dominated stands occurring mainly in the Északi-középhegység Mts, characterized by species of nutrient poor soils, proposed as a new association Trifolio medii-Brachypodietum pinnati Illyés, Bauer & Botta-Dukát 2009; 5. transition towards meadows and successional stands dominated mainly by Brachypodium pinnatum.