This study was conducted to determine whether standard and dwarfing sweet cherry rootstocks under water deficit conditions respond differently relative to plant growth and gas exchange parameters, water-use efficiency, and leaf carbon isotope composition. One-year-old potted sweet cherry cv. `Rainier' grafted on the standard rootstock `Mazzard' and on the dwarfing rootstock `Gisela 5' were compared under two different water treatments: 1) well-watered, which received daily 100% of the amount of water lost by ET, and 2) a water deficit treatment, which received 50% of the water applied to the control. Relative shoot growth rate, leaf emergence rate and cumulative leaf area were recorded every three to seven days during the experiment. Leaf net carbon dioxide assimilation rate, stomatal conductance, transpiration rate, internal CO2 concentration, and WUE were measured daily for the duration of the experiment. At the end of the experiment, leaf samples were collected to determine leaf carbon isotope composition. The growth parameters measured were affected similarly in the two rootstocks indicating a similar degree of sensitivity to water deficit in the genotypes tested. Cumulative leaf area was affected earlier by water deficit than relative shoot growth, and leaf emergence rate. Gas exchange parameters were affected earlier than growth parameters. Overall, WUE was not significantly different between dwarfing and standard rootstocks, and did not appear to increase under water deficit condition, indicating that irrigation should be considered as an important practice in sweet cherry orchards, especially when dwarfing rootstocks are selected.