VvMADS9, a MADS-box gene, from grapevine (Vitis vinifera L.) cultivar Cabernet Sauvignon has been isolated and its expression pattern studied in wild type Cabernet Sauvignon, Mourvèdre, and Bouchalès cultivars and mutants of the latter two genotypes showing abnormal petal / stamen structures. Sequence analysis showed that VvMADS9 was highly similar to PISTILLATA (PI), the class B gene that specifies the identity of petals and stamens in Arabidopsis. The temporal expression pattern of VvMADS9 studied through real-time PCR revealed that its expression was specific to flower development. The low levels of expression in the Mourvèdre mutant and the skewed expression pattern in the Bouchalès mutant as compared to their wild type counterparts suggested that VvMADS9 is involved in normal formation of petals and stamens. Through in situ hybridisation, expression of VvMADS9 was detected in stamens and weak expression on the basal regions of the petals. This suggested a possible role for VvMADS9 in specifying stamen and petal organ identity in grapevine similar to Class B genes in other species. All evidence thus pointed to the conclusion that VvMADS9 is an orthologue of PISTILLATA in grapevine.