Objective: Parents play an important role in children’s illness management, in promoting child adjustment and reducing behavior problems. Little research has focused on the evaluation of parenting interventions in the context of childhood chronic illness. The aim of this study was to test the efficacy of a brief, group parenting intervention (Healthy Living Triple P) in improving parenting skills and parent adjustment, and reducing child behavioral and emotional difficulties in the context of childhood asthma and eczema. Method: One hundred seven parents of children with a diagnosis of asthma and/or eczema were randomly assigned to intervention (n = 52) or care as usual (CAU; n = 55). Parents completed self-report measures of their child’s behavioral and emotional adjustment, their own parenting, and their own level of adjustment at pre- and postintervention and at 6-month follow-up. Parent–child interactions were observed and coded at each time point. The intervention consisted of 2 group sessions of 2 hr each delivered by trained, accredited practitioners. Results: Attrition was low, with T2 and T3 assessment completed by 84.6% and 80.8% of intervention families and 92.7% and 81.8% of CAU families, respectively. Intention-to-treat analyses indicated that overall parent-reported ineffective parenting as well as parental overreactivity reduced as a result of intervention. Parent report of child behavior problems also decreased, but there were no changes in children’s emotional adjustment. No changes in observed parent or child behavior were found. Stress reduced for parents in the intervention group compared to the CAU group, but there were no changes in parental anxiety or depression. Effects showed evidence of reliable and clinical change and were maintained at 6-month follow-up. Conclusions: The intervention shows promise as an addition to clinical services for children with asthma and eczema and may have broader application to other chronic health conditions.