Previous studies have indicated that patients scheduled for orthognathic surgery tend to have lower maximum bite forces and exert lower forces during mastication. The effect of these deficits on masticatory performance have not been previously assessed. Masticatory performance was analyzed in four groups: male and female orthognathic surgery patients prior to presurgical orthodontics (n = 12 and 23), and male and female controls (n = 27 and 31). Mastication performance was analyzed by having the subjects chew 5-g pieces of carrot for 20 cycles and measuring the resulting median particle size with a standard sieve method. Masticatory performance showed the same trends as maximum bite force and masticatory forces: male controls had the best and patients the poorest masticatory performance. There was a weak correlation between masticatory performance and maximum bite force at the molar positions. Masticatory performance also weakly correlated to electromyographic signals during mastication of a constant bolus (gummy bears) for all muscles except the left posterior temporalis. Correlations were generally not present or were very weak between masticatory performance, estimated masticatory forces, and muscle efficiency, suggesting that muscle efficiency and forces generated during mastication are not the primary factors that determine masticatory performance. Other factors contributing to a person's ability to chew food might include occlusal relationships and mechanical advantage.