Clients 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.