Background Sweden has a comparatively extensive treatment system for handling alcohol and drug problems in terms of beds in inpatient treatment and number of outpatient facilities (Klingemann, Takala, & Hunt, [...], This article compares the roles of two different addiction treatment systems, one in Stockholm county, surrounding the Swedish capital, and the other in a county in Northern California, in relation to marginalized and socially integrated misusers. It investigates: (a) whether the Swedish treatment system, as suspected, treats more marginalized clients than the American system, (b) where in the two systems those with stronger or weaker social ties show up, and (c) what kind of formal and informal pressures the socially marginalized and more integrated groups experience. The analyses are based on structured interviews with two representative samples of clients/patients entering different parts of the treatment systems (926 persons in the Californian county in 1995, 1,865 persons in Stockholm county 2000-2001). The Stockholm county treatment system has a much higher share of marginalized persons than the Californian, and a large proportion in California, almost one third, has both a job and a stable housing (15% in Stockholm). The Stockholm clients were considerably older. Drug use was connected with a marginalized position in both countries, and particularly so in Stockholm. The socially integrated in Stockholm stood out as the group with the highest share of alcohol-dependent persons, the highest Addiction Severity Index (ASI) alcohol scores, and the highest amount of heavy drinking. In both sites, the marginalized had more treatment experience and were more often found in inpatient treatment. There was a somewhat clearer social division in the U.S. system than in the Swedish. Some reasons for this are discussed, including the relation of the treatment system to other handling systems. KEY WORDS: Treatment systems, marginalization, social integration, Sweden, USA.