Objectives The aim of this study was to pilot test the effectiveness of reminders versus no intervention for increasing the number of translated Cochrane plain language summaries (PLSs) among volunteer translators.

Study design Parallel-group randomised controlled trial.

Setting Cochrane Croatia translation project.

Participants Adults who volunteered to translate Cochrane PLSs within the Cochrane Croatia translation project.

Intervention The participants were randomly allocated to intervention (receiving up to four bi-weekly email reminders to translate PLSs) or control group (no intervention).

Primary outcome The number of translated PLSs within the 6-month trial period.

Results We included 80 participants. The median number of translated PLSs after 6 months was 9 in the intervention group (95% CI 2.0 to 15.0) and 4 in the control group (95% CI 2.9 to 7.0), but this was not significantly different (p=0.181, Mann-Whitney U test). There was no difference between the groups in the number of translations after 3 months, the average time-to-translation after 3 or 6 months, or the satisfaction at the end of the study period. The number of reminders received and the number of translated summaries were negatively correlated (r=−0.50; 95% CI −0.70 to −0.22).

Conclusions Our pilot trial showed that reminders do not seem to be significantly effective in increasing the number of PLS translations. Future studies could explore whether different frequency, timing and content of reminders have an influence on an increase in the engagement among volunteer translators of evidence synthesis.

Trial registration NCT03534791.