Early season defoliation of maize significantly reduced plant height and leaf area index but leaf number and leaf emergence rate were not affected. Ear development was significantly affected by both early and late season defoliation although tassel development was barely influenced. Silk growth was the phase of ear development most sensitive to defoliation. Early season defoliation significantly reduced all yield components, leading to yield losses ranging from 54 to 100%. The position of the leaves which were removed had an important effect on the final grain yield. Harvest index was affected by both the intensity and timing of defoliation.