Background Theory of Mind (TOM) has rarely been studied in people with intellectual disabilities. Wherever it has been studied, differing results have been found. These may be attributed to a variety of factors (e.g. the different chronological ages of samples). The validity of relating TOM performance to social behaviour has also been questioned in this population. The aim of this study was to compare TOM scores with chronological age and social ability in an attempt to contribute to current debate. Methods Twenty children were matched individually with 20 adults, all with non-speci®c intellectual disabilities. The British Picture Vocabulary Scale, Raven's Coloured Progressive Matrices and four TOM tasks were administered to the participants. Their carers were then given various sociability measures to complete. Results The children achieved signi®cantly higher TOM scores than did the adults. TOM and social ability were signi®cantly positively correlated for the children, but not for the adults. These results are discussed in terms of the different social experiences of adults and children with intellectual disabilities. Conclusions Longitudinal research in this area is needed to clarify the present ®ndings. If con®rmed, the suitability of some TOM tasks used may be questionable, and there are clear implications for staff and client training.