TIR1 and its homologues act as auxin receptors and play a crucial role in auxin-mediated plant development. While the functions of auxin receptor genes have been widely studied in Arabidopsis thaliana, there has been no report on the consequences of TIR1 overexpression in plants that regulate fruit development. Here a putative tomato auxin receptor gene, homologous to Arabidopsis AtTIR1, is reported. This gene, designated as Solanum lycopersicum TIR1 (SlTIR1), was found to be expressed in all the parts of floral buds and flowers at anthesis stages. From bud to anthesis, SlTIR1 expression increases slightly in sepal tissue and decreases dramatically in stamen. From anthesis to post-anthesis when fruit set is expected to occur, the expression of SlTIR1 declines in the ovary and sepal. Overexpression of SlTIR1 results in a pleiotropic phenotype including parthenocarpic fruit formation and leaf morphology. Furthermore, SlTIR1 overexpression altered transcript levels of a number of auxin-responsive genes. The present data demonstrate that the tomato SlTIR1 gene plays an important role at the stages of flower-to-fruit transition and leaf formation.