Given the consistent findings of theory of mind deficits in children with autism, it would be extremely beneficial to examine the profile of theory of mind abilities in other clinical groups such as fragile X syndrome (FXS) and Down syndrome (DS). The aim of the present study was to assess whether boys with FXS are impaired in simple social situations that require them to understand their own and others mental states in essence: do they have a theory of mind? Well-standardized tasks of theory of mind, the location change false belief task and the appearance/reality tasks were employed to examine whether any impairment might be specific to the FXS or part of a more generalized developmental deficit. The results suggest that children with FXS do have impairment in theory of mind that is comparable to the deficit reported in other groups with learning disabilities such as DS. However, closer inspection of the impairment between these groups revealed qualitative differences in error types (realist vs. phenomenist), suggestive of atypical development that goes beyond general cognitive delay. The findings are discussed in terms of the teasing apart of different components of social cognition in order to identify syndrome-specific deficiencies and proficiencies.