Background:There is a growing body of research linking sedentary behavior with increased risk of chronic disease and all-cause mortality. It is increasingly recommended that service providers address the multiple behavioral risk factors associated with these chronic diseases as part of routine substance abuse treatment. Objectives:The study objective was to investigate rates of physical activity and sedentary behavior in a residential substance abuse population. In addition, efficacy of a sedentary behavior intervention, “Sit Switch,” was examined for feasibility in this context. Methods:Participants (n = 54) were residents of The Salvation Army Recovery Service Centres located in Canberra and on the Gold Coast, Australia. Actigraph GT3X+ accelerometers were used to measure rates and patterns of sedentariness and physical activity. A nonrandomized controlled study of a single-session group intervention aimed at decreasing prolonged sitting (“Sit Switch”) was conducted. Education, motivational-interviewing, and goal setting components underpinned the “Sit Switch” intervention. Results:Individuals were highly sedentary, spending 73% of daily activity at sedentary intensity engaged in inadequate levels of moderate physical activity (6.6%/day). The single session educational program did not lead to any significant changes in sedentary behavior. Conclusion/Importance:High levels of sedentariness and low levels of physical activity engagement are evident in residents in substance abuse treatment programs. It is strongly recommended that sedentariness, a modifiable risk behavior with independent consequences for cardiovascular disease and cancer, be addressed within residential programs.