Allium brussalisii, from Mount Parnitha near Athens (Sterea Hellas, Greece), is described as a species new to science and compared with related species of Allium section Codonoprasum and Allium section Brevispatha. It is a diploid species (2n = 2x = 16) that flowers in early autumn. On the basis of its unilateral and more or less entire spathe and the simple filaments, it resembles species of Allium section Brevispatha; however, its sectional taxonomy remains unclear as, on the basis of several other morphological, cytological, and ecological characteristics, it also resembles species of Allium section Codonoprasum. The new species is presently known only from the type locality and is of particular interest for the phylogeny of the genus. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 140–146.