A comparative study of asymmetries in cerebral width was conducted in a sample of great apes, Old World and New World monkeys. The brains of all subjects were scanned using magnetic resonance imaging (MRI) and the first axial slice above the third ventricle was identified. Measures of cerebral width were taken at distances of 10% and 30% of the length from the occipital and frontal poles. Cerebral widths were measured from the midline to the lateral surface of the brain for each area. The great apes exhibited a right-frontal and left-occipital directional asymmetry in cerebral width. In contrast, no significant mean directional asymmetries were found in either the Old or New World monkeys. The results in the great apes are consistent with previous reports of petalia asymmetries and suggest that the use of MRI is a valid approach to the assessment of neuroanatomical asymmetries in primates.