Aim: To introduce and assess a novel method for measuring washout resistance of cement-based dental materials, including mineral trioxide aggregate (MTA), to qualitatively verify the results with a clinical simulation and to evaluate the washout resistance of a new root-end filling material.  Methodology: A method for assessment of washout resistance of root-end filling materials was developed by adapting the CRD-C 661-06 (a method for evaluating the resistance of freshly mixed concrete to washout in water), to permit testing of dental cements. White Portland cement (PC), MTA-Plus mixed with either water or a polymer-based anti washout gel (MTA-AW), MTA-Angelus, IRM and amalgam were tested with either distilled water or HBSS as washout media. Additionally, the washout resistance was
tested qualitatively by spraying the test materials at the terminus of simulated canals with a metered jet of water. Results: A mass loss of 2–7% for PC, 0.4–4% for MTA-Plus, 0.9% for MTA-AW, 5–10% for MTAAngelus and 0% for IRM and amalgam was recorded with the modified CRD-C 661-06 method. No significant difference was found between using water and HBSS as washout media for the same material. The results of the modified CRD-C 661-06 method were similar to those obtained on the simulated canals. Conclusions: The modified CRD-C 661-06 method provided repeatable results that were comparable to the simulated clinical method. The anti washout gel used with MTA-Plus reduced the material washout and was similar to IRM and amalgam. (International Endodontic Journal 2012; 46: 179-186)