Background: Across studies and across outcomes, parents of children with Down syndrome have been found to experience greater well-being than parents of children with other intellectual disabilities (ID). This study examined the extent to which differences in family income and child temperamental difficulty can explain why parents of children with Down syndrome experience greater well-being. Method: Fifty married couples who were parents of young children with ID completed a set of questionnaires measuring child temperament, parent satisfaction with social support, depression and parenting beliefs. Parents were observed interacting with their children. Results: When groups were compared without consideration of demographic differences, the findings generally replicated the Down syndrome advantage found by other researchers. After variance attributable to income was removed, however, the Down syndrome advantage disappeared for all parenting and parent wellness measures. The effects of child temperament were confined to maternal and paternal depression. Conclusions: Family income was more important than child etiology in predicting the parent measures used in the study.