Objective: There are indicators that parental psychological factors may affect how parents evaluate their child’s quality of life (QoL) when the child has a health condition. This study examined the impact of parents’ perceived stress on parent and child ratings of the QoL of children with ADHD. Method: A cross-sectional sample of 45 matched parent–child dyads completed parallel versions of the KIDSCREEN-27. Children were 8 to 14 years with clinician diagnosed ADHD. Results: Parents who rated their child’s QoL lower than their child had higher perceived stress scores. Parent stress was a unique predictor of child QoL from parent proxy-rated but not child-rated QoL scores. Conclusion: Parents’ perceived stress may play an important role in their assessments of their child’s QoL, suggesting both parent and child perspectives of QoL should be utilized wherever possible. Interventions that target parent stress may contribute to improvements in the child’s QoL.