Changes in plant architecture have been central to the domestication of wild species. Tillering or the degree of branching determines shoot architecture and is a key component of grain yield and/or biomass. Previously, a tiller inhibition mutant with a monoculm phenotype was isolated, and the mutant gene (tin3) was mapped in the distal region of chromosome arm 3A^mL of T. monococcum. As a first step towards isolating a candidate gene for tin3, the gene was mapped in relation to physically mapped ESTs and STS markers developed based on synteny with rice. In addition, we investigated the relationship of the wheat region containing tin3 with the corresponding region in rice by comparative genomic analysis. Wheat ESTs that had been previously mapped to deletion bins provided a useful framework to identify closely related rice sequences and to establish the most likely syntenous region in rice for the wheat tin3 region. The tin3 gene was mapped to a 324-kb region spanned by two overlapping BACs of rice chromosome arm 1L. Wheat-rice synteny was found to be exceptionally high at the tin3 region despite being located in the high-recombination, gene-rich region. Identification of tightly linked flanking EST and STS markers to the tin3 gene and its localization to highly syntenic rice BACs will assist in the future development of a high-resolution map and map-based cloning of the tin3 gene.