Objective: The goal of this study was to test the degree to which client clinical characteristics and environmental context and social workers' practice values and experience influenced support for client's autonomy and willingness to engage in shared decision making (SDM), and whether willingness to engage in SDM was mediated by support for autonomy. Method: A randomized factorial survey of social workers working with adults with severe mental illness was employed. Eighty-seven social workers responded yielding 435 vignettes. Results: Hypotheses were partially supported. Diagnosis, symptomology, threats of harm, treatment adherence, substance use, and social workers' values and experience predicted support for autonomy and willingness to engage in SDM. Willingness to engage in SDM was modestly mediated by support for autonomy. Conclusion: Helping social workers avoid bias in decision making is critical to the goal of supporting clients' autonomy, building their capacity, minimizing disempowerment, and promoting recovery.