BackgroundClients diagnosed and treated for Chlamydia trachomatis are a recognised high-risk group for subsequent infection. An estimated 8% of clients treated for chlamydia at Cairns Sexual Health Service return for re-testing within the recommended 3-4-month period. There is no recall or reminder system in place. This study assesses the effectiveness of using short messaging service (SMS) reminders with and without incentive payments to increase re-testing rates.MethodsEligible consenting clients were randomly allocated to one of three groups. Group 1 (controls) received the standard advice from the clinician to return for re-testing in 3-4 months. Group 2 received the standard advice and an SMS reminder at 10-12 weeks post-treatment. Group 3 received the standard advice and the SMS reminder, which also offered an incentive payment on clinic attendance.Results32 participants were recruited to groups 1 and 2 and 30 participants to group 3. 62 SMS reminders were sent with 13 (21.0%) reported as undelivered. Re-testing rates were 6.3%, 28.1% and 26.7% for groups 1, 2 and 3, respectively.ConclusionSMS reminders with or without an incentive payment increased re-testing rates in our clients who were diagnosed and treated for chlamydia. However, re-testing remained less than ideal, and the high rate of undelivered SMS reminders suggest that this intervention alone will not achieve desired re-testing rates and that a range of strategies will be required to increase re-testing in this population.