The trial was carried out in 2003 on Frantoio and Leccino trained according to the monocone systems with a plantation density of 555 plants ha-1. The irrigation treatments were a rain-fed control, and three treatments that received a seasonal irrigation amount of 33, 66 and 100% of crop evapotranspiration (ETc) starting from the beginning of pit hardening. Leaf water potentials and maximum stomatal conductance of plants subjected to deficit irrigation treatments (33 and 66% of ETc) did not differ markedly from those of fully irrigated plants, while rain-fed plants showed the typical detrimental effect of water stress. However, at harvest fruit number, and mean fruit weight showed a linear enhancement according to the irrigation volume. Differences in yield between treatments seemed to be mainly related both to fruit mean weight and number, indicating that the water availability might have affected rather growing conditions before flowering or during the early stages of fruit growth than later in the season. The effects of irrigation on histological features of flesh tissues of ripe fruits were also studied. Lipid content and composition, phenolic compounds, and organoleptic characteristics were not affected by irrigation treatments. In these experimental conditions, delaying the irrigation start may enable growers to save water while maintaining yield of their olive orchards.