Utilization of emergency department (ED) services and hospitalization among a cohort of substance abusers are described based on structured research interviews with 470 adults without primary care admitted to an urban residential detoxification program. Cross-sectional analysis of baseline data of subjects found nearly 19% of subjects went to an ED on 2 or more occasions in the 6 months prior to detoxification and 14% were admitted for an overnight hospitalization. Upon further analysis of past 6-month ED utilization, the following factors were independently associated with increased odds of ED use: White race; at least one month homeless in the past 5 years chronic health condition; injury in past 6 months; and subject perception that their substance abuse interfered with seeking care from a regular doctor. Subjects with cocaine as a primary problem had lower odds of ED utilization than a reference group with alcohol as a primary problem.