During the past nine years many specialized addiction assessment/referral services have been established in Ontario. These services are expected to receive referrals from all sources, to conduct thorough socio-behavioural assessments, to refer clients to appropriate community resources and to provide case management services appropriate to client needs. Although definitive statements concerning the assessment/referral services are considered premature, the available data suggests that they are generally similar to other types of addiction services with respect to referral sources and client characteristics. However, assessment/referral services are less likely to be restricted to particular types of clients, more likely to use structured assessment procedures and to make referrals to other services. There are significant differences between individual assessment/referral services, particular with respect to referral sources, client characteristics and operating procedures and the extent to which they also provide treatment. These differences partly reflect differences in operating environments. Most communities with assessment/referral services lack generally accessible outpatient services and it remains to be seen how assessment/referral services will evolve as more outpatient services become available. Data from a 1986 survey showed that assessment/referral services saw about 10% of all cases seen within Ontario's specialized addiction treatment system but they were not significant points of entry into this system.