Objectives To investigate the use of the digital pen (DP) system to collect data in a clinical trial. To assess the accuracy of the system in this setting. Design Qualitative study based on semistructured interviews and a focus group. Quantitative study comparing the DP system and a double manual data-entry system in accuracy of acquiring data by variable type (tick boxes, dates, numbers, letters). Setting An ongoing randomised multicentric clinical trial in tertiary care in France. Participants 27 investigators involved in the trial (anaesthetists) who did or did not include patients, 4 study monitors and the study coordinator. Results Six key findings emerged: 1) the DP system was easy to use; its utilisation was intuitive, even for investigators inexperienced in informatics; 2) despite its portability, the DP was not always used in front of patients; 3) the DP system did not affect patient recruitment; 4) most of the technical problems of the system occurred during setup (compatibility, password access, antivirus software); 5) the main advantage was quickness of data availability for the study coordination staff and the main hindrance was the extra time required for online verification; and 6) all investigators were ready to use the system again. The investigators had to check 16% of data obtained by the DP system during the verification step. There is no relevant difference between the number of errors for the DP and the double manual data-entry systems: 8/5022 versus 6/5022 data entries. 5 out of 8 DP-system failures were due to the intelligent character recognition system. Conclusion The DP system has a good acceptability among all investigators in a clinical setting, whether they are experienced with computers or not, and a good accuracy, as compared with double manual data entry.