Aims. To evaluate the effectiveness and value of social services added to standard addiction rehabilitation. Design. A controlled, quasi-experimental, field study with repeated measures. Setting. Conducted in two groups of publicly supported outpatient addiction treatment programs. Control programs provided standard, twice-weekly, outpatient group counseling. "Enhanced" programs provided standard counseling but also case managers to coordinate and expedite use of pre-contracted medical screenings, housing assistance, parenting classes and employment services. Measurements. The Addiction Severity Index was used to record the nature and severity of patient problems in seven areas at treatment admission and at 6-month follow-up. Services provided during treatment were measured with the Treatment Services Review. Measures were taken on consecutive samples of patients admitted to all programs-before enhancements (wave 1, N = 431)-and at 12 months (wave 2, N = 710); and 26 months following enhancements (wave 3, N = 187). Findings. There were no significant differences in patient characteristics, treatment services or 6-month outcomes of the two sets of programs in wave 1. Wave 2 and especially wave 3 enhanced programs provided significantly more social and medical services than control programs. Patients treated in enhanced programs showed significantly less substance use, fewer physical and mental health problems and better social function at 6-months than Controls. Conclusions. Adding social services to public sector programs substantially improved the outcomes of addiction treatment. Changes in "real world" systems require time to implement; early evaluations may fail to capture the full impact of those changes.