Mothers of children with Down syndrome, autism, and mixed etiology intellectual disabilities, matched on child age, gender, and communication skills (n = 19 in each group) completed measures of their child's adaptive and problem behaviors, their own parenting stress, and positive perceptions of their child. Children with autism were rated as having more problem behaviors and lower levels of social competence than children with Down syndrome and mixed etiology intellectual disabilities. Mothers of children with autism scored lower on positive perceptions of their child, and higher on stress than the other two groups. After selecting closely matched groups, we found several group differences in child behavior but little evidence of group differences in maternal outcomes.