The primary outcome is the trajectory of opioid use since START entry, operationalized as number of days using opioids per month over the follow-up period since START enrollment. Other long-term outcomes of interest will include alcohol and other drug use, mental and physical health, quality of life, criminal justice status, HIV/HCV risk behaviors, and mortality. Treatment access and utilization factors of interest will include: predisposing personal factors, treatment experiences, and perceptions and attitudes toward treatment. Other correlates of interest will include cognitive functioning, mental health functioning, and social support.