OBJECTIVES: Painful vaso-occlusive episodes (VOE) are the most common reason for emergency department (ED) visits experienced by patients with sickle cell disease (SCD). The National Heart, Lung and Blood Institute (NHLBI) evidence-based recommendations for VOE treatment are based primarily on expert opinion. In this randomized controlled trial (RCT), we will compare changes in pain scores between patients randomized to a patient-specific analgesic protocol versus those randomized to a weight-based analgesic protocol, as recommended by the NHLBI guidelines. METHODS: We report the rationale and design of a multi-site, phase III, single-blinded, RCT to be conducted in six EDs in the United States. Eligible participants will be randomized after providing consent, anticipating 50% of those randomized would have an ED visit during the enrollment period. A total of 230 participants with one VOE ED visit provides sufficient power to detect a clinically significant difference in pain score reductions of 14 between groups with 0.05 type I error. Uniquely, this trial randomizes participants in a larger population than the study population, given the impossibility of consenting and randomizing participants during emergencies. The primary endpoint is the change in pain scores in the ED from time of placement in treatment area to time of disposition (hospitalization, discharged home, or assigned to observation status) or a maximum treatment duration of 6 hours. Additional outcomes include hospitalizations and ED visits seven days post enrollment, side effects, and safety assessments. CONCLUSIONS: The COMPARE-VOE study design will provide high-level evidence to support the NHLBI VOE treatment guidelines.