In this paper, we summarize some of our findings from a series of three meta-analyses and discuss their implications for autism research. In the first meta-analysis, we examined studies addressing the theory of mind hypothesis in autism. This analysis revealed that theory of mind disabilities are not unique to autism, although what may be unique is the severity of the dysfunction in this group. Variables such as the chronological and mental age of the participants, and the matching procedures that the researchers employed, were found to be significant moderator variables. In the next two meta-analyses, data regarding siblings and parents of individuals with autism were analyzed. Type of comparison group (e.g., siblings or parents of individuals with Down syndrome or learning disabilities) and type of outcome measure (cognitive, psychiatric, language) were found to be important moderator variables. Furthermore, method of assessing the psychiatric difficulties (e.g., self-report, clinical measures) was found to be a moderator variable in parents' meta-analysis. Suggestions for future research are discussed, highlighting variables such as type of comparison group, matching procedures, chronological and mental ages, gender, and birth order.