We implement a field experiment to study the impact of reminder messages on dental health prevention. Patients who are due to schedule a check-up receive no reminder, a neutral reminder postcard, or reminders including additional information on the benefits of prevention. Our results document a strong impact of reminders. Within one month after receiving a reminder, the fraction of patients who make a check-up appointment more than doubles. The effect declines slightly over time, but remains economically and statistically significant. Including additional information in the reminders does not significantly increase response rates relative to the neutral reminder. Finally, our data indicates that applying reminders repeatedly neither strengthens nor weakens their effects.