Highlights • Children with treatment-resistant epilepsy received increasing doses of cannabidiol. • Incidence of all and major seizures was significantly reduced over 36 months. • Mean increase in seizure-free days was > 5 in each 28-day treatment period. • Cannabidiol was generally well tolerated in doses up to 50 mg/kg/day. Abstract Introduction An intermediate-sized, multicenter, expanded-access study was opened in 2015 through the support of the State of Georgia.