Introduction: We examine the association between self-reported alcohol misuse and alcohol usewithin 2 hours of having sex and the number of sexual partners among a sample of African-Americanand Latino emergency department (ED) patients.Methods: Cross-sectional data were collected prospectively from a randomized sample of all EDpatients during a 5-week period. In face-to-face interviews, subjects were asked to report their alcoholuse and number of sexual partners in the past 12 months. Data were analyzed using multiple variablenegative binomial regression models, and effect modification was assessed through inclusion ofinteraction terms.Results: The 395 study participants reported an average of 1.4 (standard error 0.11) sexual partnersin the past 12 months, 23% reported misusing alcohol, and 28% reported consuming alcohol beforesex. There was no statistically significant association between alcohol misuse and the number ofsexual partners; however, alcohol before sex was associated with a larger number of sexual partners inthe past year. Moreover, among those who misused alcohol, participants who reported alcohol beforesex were 3 times more likely to report a higher number of sexual partners (risk ratio 3.2; confidenceinterval [CI] 1.9–5.6). The association between alcohol use before sex and number of sexual partnersis dependent upon whether a person has attributes of harmful drinking over the past 12 months.Overall, alcohol use before sex increases the number of sexual partners, but the magnitude of thiseffect is significantly increased among alcohol misusers.Conclusion: Alcohol misusers and those who reported having more than 1 sexual partner were morelikely to cluster in the same group, ie, those who used alcohol before sex. Efforts to reduce the burdenof sexually transmitted diseases, including human immunodeficiency virus, and other consequences ofrisky sexual behavior in the ED population should be cognizant of the interplay of alcohol and riskysexual behaviors. EDs should strive to institute a system for regular screening, brief intervention, andreferral of at-risk patients to reduce negative consequences of alcohol misuse, including those of riskysexual behaviors.