Objective: Digital tools offer new ways of collecting outcome data in intervention research. Little is known about the potentials and barriers of using such tools for outcome measurement in multiple sclerosis trials. This study aimed to examine reporting adherence and barriers experienced by people with multiple sclerosis in an intervention study using three different digital tools for outcome measurement. Methods: This was a mixed-methods study conducted in the context of a randomized controlled trial. Data collected during the randomized controlled trial were analysed to assess reporting adherence. Twenty-three semi-structured, in-depth interviews were conducted to investigate randomized controlled trial participants’ experiences. Results: Reporting adherence was high for all three measurement tools, but lower in the control group. Four main barriers were defined: (1) the self-monitoring aspect and repeated tests imbedded in the digital tools affected participants’ behavior during the randomized controlled trial. (2) Self-monitoring caused some participants to worry more about their health. (3) Passively collected data did not always correspond with participants’ own experiences, which caused them to question the validity of the collected data. (4) Daily reporting using different digital tools placed a significant burden on participants. Conclusion: The study indicates a high reporting adherence using digital tools among people with multiple sclerosis. However, future studies should carefully consider the overall burden imposed on participants when taking this approach. Measures should be taken to avoid the potential unintended effects of the self-monitoring and gamification aspects of using digital tools. These measures could include passive monitoring, reducing the frequency of reporting and blinding participants to their own data.