The objective of this experiment was to determine how yield, size, and quality of fruit would respond to mechanical topping and manual pruning of mature `Frost nucellar' navel orange (Citrus sinensis) trees. Mechanically topping trees at 4.3 m (14 ft) or 4.9 m (16 ft) produced annual fruit yields and quality similar to that of untopped trees. Over the 4 years of this experiment, trees that were not manually pruned produced as much or more of the most valuable fruit sizes than either the severe or moderate manual pruning treatments without the associated pruning costs. Manual pruning did not improve fruit grade compared to unpruned trees. A highly significant positive and linear relationship was found between numbers of commercially valuable fruit and the total number of fruit produced annually within the range of 50,000 to 325,000 fruit/ha (20,235 to 131,528 fruit/acre). Manual pruning, which reduced total fruit numbers, reduced the number of commercially valuable fruit predictively according to this relationship.