Background: Bright IDEAS (BI) problem-solving skills training is an evidence-based intervention designed to help parents manage the demands of caring for a child with cancer. However, the resource intensiveness of this in-person intervention has limited its widespread delivery. We conducted a multicenter, randomized trial with a noninferiority design to evaluate whether a web-based version of BI requiring fewer resources is noninferior to in-person administration. Methods: 621 caregivers of children with newly diagnosed cancer were randomly assigned to standard BI delivered face-to-face or a web-based version delivered via mobile device. The primary outcome was caregiver-reported problem-solving skills. The noninferiority margin was defined as 0.2 standard deviation units of the change from baseline to end of intervention. Secondary outcomes included caregiver-reported mood disturbance, depression, and posttraumatic stress symptoms. The study was registered with ClinicalTrials.gov Identifier: NCT01711944. Findings: The effect of the standard treatment was preserved; parents in the standard BI arm improved their problem-solving (effect size = 0.53, t = 8.88, p < .001). Parents in the web-based BI group also improved their problem-solving (effect size = 0.32, t = 5.32, p < .001). Although the web-based intervention preserved 60% of the standard treatment effect, the test of noninferiority was non-significant (effect size = -0.21, p = 0.55). Similarly, the web-based intervention preserved > 60% of the standard intervention effect on all secondary outcomes; however, tests of noninferiority were non-significant. Interpretation: Noninferiority of web-based BI relative to standard face-to-face administration was not established. Further development of the web-based BI is needed before it can be recommended as a stand-alone intervention. However, the documented benefits of the web-based intervention as well as the advantages of low resource utilization and ease of delivery suggest that further development of web-based BI is indicated, and that it may play a valuable role in alleviating distress in caregivers of children with serious or chronic illness. Funding: National Institutes of Health (U.S.), R01 CA159013 (P.I.