<p style="text-align: justify;"><strong>Aims</strong>: The effects of cluster thinning on yield and extractability parameters of Syrah and Tempranillo grapes, as well as the chromatic characteristics of the wines obtained in three consecutive seasons.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Grapes of Vitis vinifera L. var. Tempranillo and Syrah were harvested from a commercial vineyard in Jumilla. Two treatments were evaluated: (a) cluster thinned, where in every shoot all the clusters, except the basal one, were removed just before veraison; (b) unthinned control. Yield, physicochemical and extractability parameters were studied in the grapes. Vinifications were made from these grapes, and chromatic parameters were studied at the end of alcoholic fermentation. Results showed that cluster-thinned vines performed better than control vines during the three consecutive years of the experiment, although the best results were obtained in the driest year (2005). The Syrah variety always provided better results than the Tempranillo variety. The cluster-thinning treatment also influenced the chromatic characteristics of the wines obtained.</p><p style="text-align: justify;"><strong>Conclusions</strong>: The results showed that thinning successfully reduced yield and produced an earlier harvest in the two varieties studied. The grape quality improved and, in general, wines made from cluster-thinned vines of both Syrah and Tempranillo had significantly better chromatic characteristics than control wines.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This study demonstrate that the practice of cluster-thinning may be recommended depending on several factors, as the varieties and the climatic conditions play also a role in the extractability parameters of grapes, and therefore its use cannot be generalized.</p>