Background: Only a minority of subjects with substance use disorders (SUDs) are in addiction-specific treatment (treatment gap). Co-operation between an unemployment office and a psychiatric hospital was established for the assessment and counseling of long-term unemployed clients with SUD. We aim at validating whether such a treatment gap exists in that group, and whether clients from an unemployment office differed from a matched group of inpatient detoxification patients with regard to socio-economic characteristics, substance use and treatment history, and the prevalence of mental disorders Methods: Unemployment office clients (n = 166) with an SUD were assessed using a standardized sociodemographic and clinical interview. They were compared with 83 inpatients from a local detoxification ward, matched for age, sex, and primary addictive disorder (matching ratio 2:1). Results: Most (75.9%) subjects were males, with an average age of 36.7 years. The SUDs mostly related to alcohol (63.9%) and cannabis (27.7%). Although most unemployment office clients had a long SUD history, only half of them had ever been in addiction-specific treatment during their lifetime, and only one in four during the last year. There were no statistically significant differences between the groups regarding age at onset of problematic substance use, the proportion of migrants, and prevalence of comorbid mental disorders. The unemployment office sample showed lower levels of education (p < 0.001), job experience (p = 0.009), and current employment rates (p < 0.001). Conversely, inpatients showed lower rates of imprisonment (p < 0.001), more inpatient detoxification episodes (p < 0.03); and longer abstinence periods (p < 0.005). Conclusions: There was a lifetime and recent treatment gap in the group of long-term unemployed subjects with alcohol and cannabis dependence. The markedly lower educational attainment, chronic employment problems and higher degree of legal conflicts in the client group, as compared with patients in detoxification treatment, might require specific access and treatment options. The co-operation between the psychiatric unit and the unemployment office facilitated access to that group.