The research presented here reports on sustainability of the practices within the National Implementing Evidence Based Practices Project for people with serious mental illness. Forty-nine sites completed the initial 2-year implementation phase and were the focus of our study. Our aims were to discern the number of sites that sustained practices 2 years after implementation, the reasons for sustaining or not sustaining, differences in characteristics between the two groups, and the extent and nature of practice adaptations. We used a mixed-methods approach, based on a telephone survey that gathered qualitative and quantitative data from site representatives and others familiar with the sites and practices during the follow-up period. We found that 80% of sites sustained their practices for 2 years post-implementation, that sustainers differed from non-sustainers in several domains: financing, training, fidelity and agency leadership, and that most sites adapted practices moderately to meet state and local needs.