Tillering is one of the most important agronomic traits in cereal crops, because tiller number per plant determines spikes or panicles per plant, a key component of grain yield and/or biomass. In order to characterize the underlying genetic variation for tillering, we have isolated mutants that are compromised in tillering ability using ethyl methanesulphonate (EMS) based mutagenesis in diploid wheat (Triticum monococcum). The tillering mutant, tiller inhibition (tin3) produces only one main culm compared to the wild type with many tillers. The monoculm phenotype of tin3 is due to a single recessive mutation. Genetic and molecular mapping in an F₂ population of diploid wheat located the tin3 gene on the long arm of chromosome 3A^m. One codominant RFLP marker Xpsr1205 showed cosegregation with the tin3 in the F₂ population. Physical mapping of the cosegregating marker Xpsr1205 in a set of Chinese Spring deletion lines of group-3 chromosomes placed the tin3 gene in the distal 10% of the long arm of chromosome 3A, which is a recombination-rich region in wheat. Identification and genomic mapping of the tin3 gene in the distal high recombination region of chromosome arm 3AL is the first step towards map-based cloning of the tillering gene in wheat.