The US Department of State estimates that there are between 4 and 27 million individuals worldwide in some form of modern slavery. Recent studies have demonstrated that 28 percent to 50 percent of trafficking victims in the United States encountered health care professionals while in captivity, but were not identified and recognized. The 20 largest San Francisco Bay Area EDs were randomized into intervention (10 EDs) or delayed intervention comparison groups (10 EDs) to receive a standardized educational presentation containing the following: background about HT, relevance of HT to health care, clinical signs in potential victims, and referral options for potential victims. Participants in the delayed intervention group completed a pretest in the period the immediate intervention group received the educational presentation, and all participants were assessed immediately before (pretest) and after (posttest) the intervention. The intervention effect was tested by comparing the pre-post change in the intervention group to the change in two pretests in the delayed intervention group adjusted for the effect of clustering within EDs. The four primary outcomes were importance of knowledge of HT to the participant's profession (5-point Likert scale), self-rated knowledge of HT (5-point Likert scale), knowledge of who to call for potential HT victims (yes/no), and suspecting that a patient was a victim of HT (yes/no). The study determined that there were 258 study participants from 14 EDs; 141 from 8 EDs in the intervention group and 117 from 7 EDs in the delayed intervention comparison group, of which 20 served as the delayed intervention comparison group. Participants in the intervention group reported greater increases in their level of knowledge about HT versus those in the delayed intervention comparison group (1.42 vs -0.15; adjusted difference = 1.57 [95 percent confidence interval, 1.02-2.12]; P < 0.001). Pretest ratings of the importance of knowledge about HT to the participant's profession were high in both groups and there was no intervention effect (0.31 vs 0.55; -0.24 [-0.90-0.42], P = 0.49). Knowing who to call for potential HT victims increased from 7.2 percent to 59 percent in the intervention group and was unchanged (15 percent) in the delayed intervention comparison group (61.4 percent [28.5 percent-94.4 percent]; P < 0.01). The proportion of participants who suspected their patient was a victim of HT increased from 17 percent to 38 percent in the intervention group and remained unchanged (10 percent) in the delayed intervention comparison group (20.9 [8.6 percent- 33.1 percent]; P < 0.01). Thus, a brief educational intervention increased ED provider knowledge and self-reported recognition of HT victims. (Publisher abstract modified)