Revised Response Evaluation Criteria in Solid Tumours (RECIST 1.1) came into effect in 2009 in order to address the issues and limitations of RECIST 1.0. While RECIST 1.1 has addressed many challenges with the previous version, some drawbacks still remain. More than five years of clinical trials monitoring, across numerous international sites has revealed that investigators across all countries encounter many and similar difficulties in interpreting RECIST 1.1 and tend to make the same mistakes. These errors, if not timely identified and corrected, lead to increased variability of data across the trial sites and may affect efficacy endpoints. In our opinion, pro-active training, focused on typical questions/mistakes may help to increase the accuracy of the RECIST data extraction at the trial sites. Iryna Teslenko, MD Ukraine; Maxim Belotserkovsky, MD, Germany, Akhil Kumar, MD, USA PSI CRO AG, Switzerland share their thoughts on common pitfalls of RECIST 1.1 application in clinical trials.