Magnesium, a vasodilator, anti-inflammatory, and pain reliever, could alter the pathophysiology of sickle cell pain crises.Wehypothesized that intravenousmagnesiumwould shorten length of stay, decrease opioid use, and improve health-related quality of life (HRQL) for pediatric patients hospitalized with sickle cell pain crises. The Magnesium for Children in Crisis (MAGiC) study was a randomized, double-blind, placebo-controlled trial of intravenous magnesium vs normal saline placebo conducted at 8 sites within the Pediatric Emergency Care Applied Research Network (PECARN). Children 4 to 21 years old with hemoglobin SS or Sb0 thalassemia requiring hospitalization for pain were eligible. Children received 40 mg/kg of magnesium or placebo every 8 hours for up to 6 doses plus standard therapy. The primary outcomewaslengthof stay inhours fromthetimeof firststudydruginfusion,comparedusing a Van Elteren test. Secondary outcomes included opioid use and HRQL. Of 208 children enrolled, 204 received the study drug (101 magnesium, 103 placebo). Between-group demographics and prerandomization treatment were similar. The median interquartile range (IQR) length of stay was 56.0 (27.0-109.0) hours formagnesiumvs 47.0 (24.0-99.0) hours for placebo (P =.24). Magnesium patients received 1.46 mg/kg morphine equivalents vs 1.28 mg/kg for placebo (P =.12). Changes in HRQL before discharge and 1 week after discharge were similar (P >.05 for all comparisons). The addition of intravenous magnesium did not shorten length of stay, reduce opioid use, or improve quality of life in children hospitalized for sickle cell pain crisis.