Non-sagittal occlusal discrepancies such as posterior cross-bite and anterior openbite are common types of malocclusion, but studies on masticatory function related to those malocclusions have been scarce. The aim of this study was to quantify the masticatory performance in patients with non-sagittal discrepancies compared to those with normal occlusion, using both objective and subjective measures. Maximum bite force and contact area using Dental Prescale® system as a static objective assessment, Mixing Ability Index (MAI) as a dynamic objective evaluation and food intake ability (FIA) as a subjective assessment were analysed from 21 people in normal occlusion (Group N) and 64 patients with posterior cross-bite (Group C), anterior openbite (Group O) or both (Group B). The differences of the maximum bite force, the contact area, the MAI and the FIA were compared, and their correlations were figured out. The non-sagittal malocclusion groups showed lower values in the maximum bite force, the contact area, the MAI and the FIA compared to those in the normal group(P< 0·0001). Compared to Group N, Groups C, O and B showed 61·5%, 42·1% and 40·1% of the maximum bite force, and 84%, 84% and 76% of hard food FIA, respectively. However, there were no significant differences among Groups C, O and B. The MAI showed higher correlation with the FIA(r= 0·38,P< 0·01), than with the maximum bite force and the contact area (bothr= 0·24,P< 0·5). These results revealed that masticatory function in patients with non-sagittal discrepancies is significantly reduced both objectively and subjectively.