• We examined the relationships among roductivity, water use efficiency (WUE) and drought tolerance in 29 genotypes of Populus × euramericana (Populus deltoides × Populus nigra), and investigated whether some leaf traits could be used as predictors for productivity, WUE and drought tolerance. • At Orléans, France, drought was induced on one field plot by withholding water, while a second plot remained irrigated and was used as a control. Recorded variables included stem traits (e.g. biomass) and leaf structural (e.g. leaf area) and functional traits [e.g. intrinsic water use efficiency (Wi) and carbon isotope discrimination (∆)]. • Productivity and ∆ displayed large genotypic variability and were not correlated. ∆ scaled negatively with Wi and positively with stomatal conductance under moderate drought, suggesting that the diversity for ∆ was mainly driven by stomatal conductance. • Most of the productive genotypes displayed a low level of drought tolerance (i.e. a large reduction of biomass), while the less productive genotypes presented a large range of drought tolerance. The ability to increase WUE in response to water deficit was necessary but not sufficient to explain the genotypic diversity of drought tolerance.