Recent functional animal studies have reported that the motor control of masticatory muscle function is bilaterally guided by both hemispheres, which may fundamentally differ from the cortical control of limb muscle function. In this study, we investigated whether unilateral cortical brain infarction induces different impairments in masticatory and upper limb motor performance. Evidence of the importance of both hemispheres in controlling masticatory movements would be greater if the masticatory function were shown to be unimpaired in patients with severe hemiplegia. The masticatory function of 16 patients with severe hemiparesis caused by brain infarction in the region of the middle cerebral artery was studied by means of interview, clinical examination, and bite-force measurements. Finger-thumb grip-force measurements and clinical examination of the upper limbs were also performed for evaluation of the effect of infarction on upper limb motor function. Localization of the infarction was confirmed with computer tomography and magnetic resonance imaging. The Scandinavian Stroke Scale demonstrated that each patient had a major unilateral cortical infarction which had caused a marked handicap with a serious impairment of upper limb function on the contralateral side. The clinical examination revealed no major signs of temporomandibular disorders, and the masticatory muscles, when examined by palpation, contracted symmetrically. None of the patients with unilateral brain infarction showed any differences in bite forces between the healthy and paralyzed sides. These results indicate that, in hemiparetic patients, great differences may exist between the motor performances of the masticatory and upper limb muscles. The present investigation clinically illustrates the importance of both hemispheres in the control of masticatory function and movements.