Although olive trees are well known to be resistant to drought, the economic advantages of irrigation have been clearly demonstrated. Today, the olive growing areas in the Mediterranean Basin suffer from water shortages and increased competition from other sectors for the available water resources. This study was conducted in an olive tree plantation in western Turkey in 2008-2010. In the study, the effects of different irrigation levels on yield and the physiological and morphological development of olive trees (Olea europaea L. cv. Memecik) were investigated, and the optimal irrigation schedule was determined according to the findings of the study. Six different irrigation treatments were created using a drip irrigation system. The treatments were: a control (SC) in which irrigation amounts were scheduled based on the soil moisture content of the top 90cm of root depth by the gravimetric method and five treatments that received an amount of water equivalent to 25% (S0.25), 50% (S0.50), 75% (S0.75), 100% (S1.00), and 125% (S1.25) of the five-day cumulative evaporation from a class A Pan. The total amount of irrigation water applied to the treatments during the irrigation seasons ranged from 175 to 874mm; however, actual evapotranspiration ranged from 253 to 902mm. In both cases, the lowest and highest values were, respectively, in S0.25 and S1.25. Compared with the amount of irrigation water applied to SC, approximately 72% less water was applied to S0.25 and 40% more water was applied to S1.25. Yields between treatments ranged from 24.88 to 37.35kgtree-1 and from 0.47 to 0.63kgm-3, but no significant differences were detected in yield between treatments (p<0.05). Significant differences between treatments were detected in some morphological features such as shoot length, shoot diameter, canopy volume, and fruit set ratio. In contrast, no significant differences between treatments were detected in other morphological features such as number of buds on a shoot, number of flowers per bud, and number of flowers per shoot. Taking the average of the years of the experiment, the lowest and highest values for predawn, midmorning and midday measurements of leaf water potential were obtained, respectively, from S0.25 and S1.25. It was concluded from the findings of this study that irrigation of Memecik olive trees should be scheduled based on the amount of water equivalent to 25% (S0.25) of the five-day cumulative evaporation from a class A pan. Irrigation scheduling using deficit irrigation allowed considerable water savings in olives, with minimal effects on yield. (C) 2014 American Society of Civil Engineers.