OBJECTIVE: To assess the effect of electronic reminders (ERs) on response rate and time to response for the return of postal questionnaires. STUDY DESIGN AND SETTING: This open randomized controlled trial (RCT) was conducted at the University of York. Participants who were taking part in an established RCT and who provided an electronic mail address and/or mobile telephone number were eligible to take part in the study. The intervention group received ERs on the day they were expected to receive postal questionnaires. RESULTS: One hundred forty-eight participants (19 male and 129 female) aged 47±11 (range, 19-65) years were studied. About 89.2% of participants returned postal questionnaires. There was no difference in questionnaire response rates in control (64 of 74 [86.5%]) vs. intervention (68 of 74 [91.9%]), groups (relative risk=1.063, 95% confidence interval: 0.949-1.189). Median questionnaire time to response was 4 days less in the intervention group (10.0±0.2; range, 10-14 days) compared with the control group (14.0±1.4; range, 10-23 days) (χ(2)(1df)=5.27, P=0.022). CONCLUSION: ERs are useful tools for reducing participant time to response for postal questionnaires. We found little evidence for an effect of ERs on response rate for postal questionnaires.