This study compares substance use, treatment histories, and sociodemographic characteristics of patients presenting to an emergency department (ED) following a heroin overdose or seeking detoxification services for heroin and examines risk factors for a subsequent return to the ED for a substance-related problem. A convenience sample of patients presenting for an overdose or detoxification at an urban teaching ED was recruited for this study. During their ED visit, patients were interviewed regarding demographics, substance use experiences, and treatment history. Subsequently, a review of patient records for past and subsequent ED use was performed. Patients requesting detox and those with an overdose were similar in terms of prior treatment. Both groups had similar extensive polysubstance histories. As a group, however, patients presenting for detox were more likely to report use of each of three substances (benzodiazepines, opioid pain medications, and heroin) more than three times per week, compared to those presenting for overdose. Detox patients had higher scores on the 3-item Alcohol Use Disorder Identification Test-C and the drug problems scale compared to overdose patients. Overall, 28% of the patients returned to the ED within 90 days for a drug-related issue, including 8% that returned for an overdose. Factors predictive of a return ED visit included ED visits for substance use in the previous year and recent frequent heroin use. Patients requesting detox were similar in most domains to those presenting following an overdose. Notably, overdose patients were less likely to use heroin more than three times per week compared to detox patients. Both groups were equally likely to return for an SUD reason within 3-months, however for both groups, previous ED visits and recent frequent heroin use predicted a return visit.