Parent-only (PO) treatments for childhood obesity are feasible, more cost-effective and potentially easier to disseminate. The objective of this study was to determine whether a PO treatment is not inferior to a parent + child (PC) treatment for childhood obesity. Eighty parent-child dyads with an 8-12 year old overweight or obese child (>85th BMI-P) were recruited and randomized into PO or PC treatment for childhood obesity. Parents or parent-child dyads attended 5-month treatment groups. Child and parent body size, child caloric intake, and child physical activity were assessed at baseline, post-treatment, and 6-months follow-up. Noninferiority testing using mixed linear models was used to compare PO treatment with PC treatment. Results showed that the PO group was not inferior to the PC group in terms of child weight loss. Results also showed that the PO group was not inferior to the PC group in terms of parent weight loss and child physical activity, but not child caloric intake. This study suggests that a PO treatment could provide similar results to PC in child weight loss and other relevant outcomes, and potentially could be more cost-effective and easier to disseminate. Although further research is needed, this study suggests that PO groups are a viable method for providing childhood obesity treatment.