Children and adolescents with intellectual disabilities (IDs) are an identified group with postural disturbances resulting from a lack of integration among the visual, vestibular and proprioceptive systems. The insufficient level of maturity of the sensory systems is at least partly responsible for disturbances in maintaining body balance. More sway can increase the risk of falls and body injuries. The aims of the study were (1) to compare the ability to maintain the body balance of children and youth with a varying degree of ID, both with the eyes open and closed, and (2) to determine to what extent factors such as sex, level of ID, visual stimulus and body height independently affect the ability to maintain body balance in children and adolescents with ID. The study involved 131 people aged 13-21 years (65 girls and 66 boys). The participants were classified as (1) with mild disability (42 girls and 47 boys) and (2) with moderate disability (23 girls and 19 boys), based on IQ test results. Sway measures were collected with the Zebris platform, with the eyes open and closed. Sway path, sway path in anterio-posterior and medio-lateral directions and sway area were analysed. Boys with moderate ID were characterised by a significantly more sway indicating their worse postural balance ability than boys with mild ID, both in the trials with open eyes and closed ones. The type of test (eyes open/eyes closed) to a small extent had influenced the body balance of the examined children with ID. Results of analyses of covariance had showed that all analysed factors (sex, level of ID, type of the test performance and body height), irrespectively from direction of sway (sway path in anterio-posterior and medio-lateral directions), worked independently influencing body balance. It could be assumed that lower height, moderate disability and male sex are factors significantly reducing ability of maintenance of balance of children and youth with ID. © 2019 MENCAP and International Association of the Scientific Study of Intellectual and Developmental Disabilities and John Wiley & Sons Ltd.