Studies on laterality have not supported the hypothesis that well-lateralized people do better on cognitive tasks than those with ‘mixed’ or uncertain laterality. This developmental characteristic appears to be not significantly linked with specific intellectual disabilities.This study was aimed at testing relationships between laterality and cognitive performance in mental retardation. In this population, indeed, previous invesigators have reported higher incidence of nonright laterality than in nonretarded persons, particularly among males and with reference to handedness.Sample and method. We studied the incidence of different forms of laterality (eye, hand, ear, and foot modalities) in a sample of 202 persons with mild and moderate mental retardation and borderline intellectual functioning, with and without neurological impairment, aged 7 – 79 years.We used 12 laterality tasks assessing, through direct observation, four modalities (hand, eye, ear, and foot preference), as suggested by Coren (1993). The laterality score was obtained using the formula: [(total Right - total Left) / (total Right + total Left)] x 100. The scores ranged from +100 (full right lateralization) to -100 (full left lateralization). The handedness score was computed using the same formula, but taking into account only the 4 tasks regarding hand preference. Lateralization was determined for each subject using a score 50 in the two opposite directions as a cutoff point.Results. Our data, considering the overall laterality, confirmed the hypothesis of reduced right prevalence (near 50% in both sexes), but did not confirm the hypothesis of a larger proportion of left lateralized subjects than in normal ones. Instead, if we refer to handedness only, the percentage of left-handed subjects is very high, almost one fifth in males, almost one tenth in females. A significant difference by gender was found in handedness across life-span. No significant differences were found regarding the level of impairment, either for overall laterality or for handedness.Correlations between lateralization scores and performances in cognitive tests, such as Wechsler Intelligence Scales (single subtests were also taken into account), Raven’s Progressive Matrices, and the Bender Visual-motor Gestalt Test, were computed. Results show significant relations between the degree of right sidedness and some cognitive performances, but these relations are differentiated for overall laterality and hand prevalence, and they are mediated by gender and severity of mental retardation.The results are useful for enhancing theoretical comprehension of the relations between laterality and cognitive processes.