The objective of this research was to evaluate the long-term performance of enhanced anaerobic bioremediation (EAB) at chlorinated solvent sites and the occurrence of sustained treatment following EAB. A database of groundwater concentration versus time records was compiled for 25 sites with at least three years of post-treatment data. The median post-treatment monitoring period for these sites was 5.2 years, with a maximum of 11.7 years. Long-term performance was evaluated based on concentration changes from before treatment to the final year of post-treatment monitoring. Results indicate that the median concentration reduction for all 25 sites was approximately 80%, just under 1 order of magnitude. Sustained treatment, where concentrations remain suppressed after ceasing active treatment, was evaluated using a lines-of-evidence approach including analysis of rebound, statistical concentration trends after treatment, and decay rates from before and after treatment. Results indicate that sustained treatment is occurring at a majority of the sites.