Grapevines (Vitis vinifera L.) have unusual plant architecture in that the shoot apical meristem produces both vegetative structures and primordia that are capable of forming inflorescences at regular intervals. These primordia are termed ‘uncommitted’ and differentiate into inflorescences or tendrils depending on the environment in which they are produced. To investigate the molecular relationship between tendrils and inflorescences and vine architecture, we cloned a TFL1 homologue from grapevine (VvTFL1). VvTFL1 is expressed in shoot apices early in latent bud development and in buds soon after bud burst. The grapevine homologue of LEAFY, VFL, is expressed at the same stages as VvTFL1 as well as in the later stages of inflorescence development. Neither VvTFL1 nor VFL were detected in tendrils. VvTFL1 was overexpressed in tobacco and Arabidopsis to confirm that it was functionally similar to TFL1 and not the close homologue FT. Flowering was delayed significantly in tobacco and Arabidopsis transformants overexpressing VvTFL1. However, an unexpected phenotype was observed in some of the transgenic Arabidopsis lines where the floral meristem became indeterminate and a new inflorescence would emerge from within the developing silique. Our findings suggest that VvTFL1 is a repressor of floral development. The nucleotide sequence reported in this paper has been submitted to GenBank under the accession number AF378127 (VvTFL1).