In a survey of the BrachyTAG mutant population of Brachypodium distachyon, we identified a line carrying a T-DNA insertion in one of the two eukaryotic initiation factor 4A (eIF4A) genes present in the nuclear genome. The eif4a homozygous mutant plants were slow-growing, and exhibited reduced final plant stature due to a decrease in both cell number and cell size, consistent with roles for eIF4A in both cell division and cell growth. Hemizygous plants displayed a semi-dwarfing phenotype, in which stem length was reduced but leaf length was normal. Linkage between the insertion site and phenotype was confirmed, and we show that the level of eIF4A protein is strongly reduced in the mutant. Transformation of the Brachypodium homozygous mutant with a genomic copy of the Arabidopsis eIF4A-1 gene partially complemented the growth phenotype, indicating that gene function is conserved between mono- and dicotyledonous species. This study identifies eIF4A as a novel dose-dependent regulator of stem elongation, and demonstrates the utility of Brachypodium as a model for grass and cereals research.