The aim of this study was to compare sleep problem categories of children with mental retardation without general medical condition (MR-GMC), children with MR co-occurring with GMC (MR+GMC), siblings of the MR children, and the general population.

This is the first study which separates MR children with GMC and those without GMC. The Children's Sleep Habits Questionnaire was completed by their parents to assess their children's sleep practices and behaviors such as the child's sleeping habits, sleeping arrangements, sleep anxiety, night wakening, parasomnias, and daytime sleepiness.

The clusters of bedtime resistance and sleep duration, wake up, parasomnia, sleep anxiety, and other problem categories were not different between MR children without GMC and the other two control groups of general population and siblings group. Parasomnia and other problem categories were more impaired in MR+GMC group than the three groups of MR-GMC, general population, and siblings.

The lack of difference between the MR+GMC group and those in the control groups may suggest that medical predisposing factors may contribute to an increased rate of sleep problems in MR children, rather than their MR as a cause of sleep problems. Probably, management of the accompanying medical conditions of the MR children would improve their sleep; in other words, the sleep difficulties of the children with MR are more related to their general medical problems rather than their MR.