Participation in 12-step groups (12SG) during and after formal treatment fosters positive outcome among substance users. However, the effectiveness of 12SG may be limited by high attrition rates and by low participation; little is known in this area. Clinicians play an important role in fostering 12-step participation, and the insights which they develop in their practice can greatly contribute to understanding clients’ patterns of 12-step affiliation. There has been little research on clinicians' attitudes about 12-step groups or about their experiences in referring clients. This study surveyed clients (N = 101) and clinicians (N = 102) in outpatient treatment programs to examine 12-step-related attitudes and to identify potential obstacles to participation. Data were collected between May, 2001 and January, 2002 in New York City. Both client and clinician samples were primarily African-American and Hispanic; 32% of clients reported substance use in the previous month, with crack and marijuana cited most frequently as the primary drug problem. On average, clinicians had worked in the treatment field for 8 years. Both staff and clients held favorable views of 12SG. Major obstacles to participation centered on motivation and readiness for change and on perceived need for help, rather than on aspects of the 12-step program often cited as points of resistance (e.g., religious aspect and emphasis on powerlessness). Clinicians also frequently cited convenience and scheduling issues as possible obstacles to attending 12SG. Clinical implications of these findings are discussed, including the importance of fostering motivation for change, the need to assess clients' beliefs about and experiences with 12SG on a case-by-case basis, to find a good fit between clients' needs and inclinations on the one hand, and the tools and support available within 12-step groups on the other.