The aim of this study was to investigate the incidence of reinfection with sexually transmitted infection (STI) and its possible predicting factors among patients reattending a department of genitourinary (GU) medicine. The method included a retrospective study on consecutive patients re-screened for STI in a busy department of GU medicine between January 1996 and April 2005. Cox regression model was used to investigate the association of age, gender, sex group, previous STI, counselling for an STI on the last attendance, number of sexual partners in the previous attendance episode, condom use and the number for partners with whom they had unprotected sex, with STI at current screening. The results show that 302 consecutive patients with more than two attendance episodes were included in the study. Patients were mostly women (92%), younger than 35 years (80%) and heterosexual (98%). At baseline, 70 (23%) patients had STI. The incidence density of STI at the end of follow-up period was 15.69/100 person-years. Testing positive for an STI was associated with age younger than 25 years (hazard ratio 2.70 [95% confidence interval 1.70–4.57]; P = 0.000). In conclusion, our study confirmed the improvement in access to GU medicine services, encouragement of patients with an STI for re-screening on regular basis and use of novel STI counselling strategies, especially for younger patients may reduce the incidence of subsequent STI.