Background/Aims: To determine whether frequent emergency department (ED) users who enter specialized treatment programs for alcohol and/or drug problems have any characteristics that predict their future ED use. Methods: Adult patients (783 alcohol users, 405 illicit drug users) were interviewed. Data from the medical database on utilization of ED and the emergency departments' specific units for addictive diseases (EDAD) 12 months before and 12 months after the interview were linked with patient characteristics in logistic regression models. Results: Among alcohol users, prior ED/EDAD visits predicted repeat future visits to these sites (OR 11.6; 95% CI 6.5-20.5). Prior inpatient hospital care with addiction diagnosis was a predictor of future multiple visits to the EDAD only (OR 3.1; 95% CI 1.5-6.5). Among drug users, predictors of future ED/EDAD visits were use of heroin (OR 2.7; 95% CI 1.4-5.4) and prior ED/EDAD visits (OR 27.3; 95% CI 12.7-58.4). Drug users' EDAD utilization was also predicted by inpatient hospital care with addiction diagnosis. Conclusion: The strongest predictive factors of visiting ED repeatedly were previous repeat emergency care use and hospitalization with addiction diagnosis. Entering regular addiction treatment does not appear to alter the pattern of ED utilization.