Responses of grapevine vegetative growth components to mild, medium and severe soil water deficits were used to identify simple and sensitive indicators for early diagnosis of water stress. Soil water deficit was characterised as the fraction of transpirable soil water (FTSW) remaining in a water-depleted rootzone. Growth components included the number of emerged leaves on first (Ist) and second (IInd) order lateral branches, the leaf area and internode length of each phytomer of Ist order lateral branches, and the frequency of IInd order lateral branching. These components were measured in a greenhouse on Shiraz (syn. Syrah) grapevines, over a 38-day period of stabilised soil water regimes. Leaf emergence rate, final leaf area and final internode length of lateral branches I were relatively insensitive to mild and medium water deficits. They only decreased in response to severe water deficits. The frequency of IInd order lateral branching showed a similar trend, but was inhibited at severe water deficits. The leaf emergence rate of lateral branches II was highly sensitive to FTSW, and decreased even in response to mild water deficits. Because measurement of leaf emergence rate is a time consuming process, further analysis of the data was undertaken to identify a simpler but similarly effective indicator of cumulative water deficit. Accordingly, we established that the final length of lateral branches I was sensitive to medium water deficits, while the final ratio of the number of leaves on lateral branches II to the number of leaves on lateral branches I, was sensitive to even mild water deficits. Both of these composite indicators (derived variables) were relatively easy to measure and showed potential as early indicators of water deficits. They were more sensitive to FTSW than was predawn leaf water potential. Moreover, the final ratio of the number of leaves on lateral branches II to the number of leaves on lateral branches I was even more sensitive to FTSW than was stomatal conductance.