Data on the distribution of the Pannonian endemic black hawthorn (Crataegus nigra Waldst. et Kit.) have been partly incorrect or uncertain. Older publications contain several confusions involving this species, the morphologically similar Crataegus pentagyna, and Crataegus ×degenii (C. nigra × C. monogyna). In this study, we review and evaluate records reported in the relevant literature as well as herbarium specimens. Current occurrences and population sizes were investigated through field surveys. We delineate the currently known distribution range of the species, which is restricted to the floodplain of the Danube between Budapest and the Iron Gate Gorge (Vaskapu), as well as to the vicinity of the mouths of the two major tributaries of the Danube, the Drava and the Sava. At present, the species is rare north of Gemenc and south of the mouth of the Tisza, and is probably extinct in the Belgrade region. Large populations occur in the Gemenc area (Hungary), the Kopački Rit–Apatin region (Croatia/Serbia), and the Kovilj–Gardinovci area (Serbia). The species is rapidly declining north of Gemenc owing to the desiccation of its habitats, hybridization with Crataegus monogyna, and the wide­spread invasion of alien plant species. Its conservation status in this region should be considered Criti­cally Endangered, whereas elsewhere it is more appropriately classified as Endangered.