Background The observation of STI in HIV-patients has triggered a STI-Surveillance in AIDS Reference Centres (ARC). The aim of this surveillance is to identify STI emerging in HIV-patients, to analyse STI-trends in this group and to describe patient characteristics. Methods There are nine ARC in Belgium. The ARC are specialised in HIV-patient care, STI-consultation and treatment. Since April 2007, seven ARC participate in the surveillance. STI included are limited to Chlamydia, gonorrhoea , syphilis, Lymphogranuloma Venerum (LGV), hepatitis B (HBV) and hepatitis C (HCV) among men having sex with men (MSM). Results In 2008, 6962 HIV-patients (36.8% women; 63.2% men) were followed and 7454 patients (35.7% women; 63.9% men) in 2009. The HIV-population under follow-up increased by 7.1% (8.3% in men; 4.7% in women). In 2008 as well as in 2009, 279 STI were reported among the HIV-patients. It concerns 250 men and two women in 2008 and 251 men and two women in 2009; 242 were MSM in 2008 and 244 in 2009 (96%). The finding observed in 2009, with 5.3% HIV-infected men presenting an STI vs 5.7% in 2008 prevails a lower incidence of STI. This decrease is not statistically significant (χ 2 =0.76, a=0.38). In 2008 as well as in 2009, 13 patients were diagnosed with more than 1 STI (4.6% of the STI patients) The most frequent STI was syphilis, with 171 cases (61% of STI diagnosis) in 2008 and 160 cases (59%) in 2009, of whom one woman; respectively 94% and 95% of the men were MSM. Chlamydia has been found in 30 men and two women in 2008 and in 28 men and one woman in 2009. LGV was confirmed in 12 men in 2008 and in 15 in 2009. Gonorrhoea was found in 29 men in 2008 and 32 in 2009. HBV and HCV were respectively diagnosed in 2 and 14 men in 2008 and in 7 and 17 men in 2009. All men reported with Chlamydia, LGV, gonorrhoea, HBV and HCV were MSM. 64% (2008) and 75 % (2009) of the homosexual men with STI mentioned having multiple partners. Conclusions The surveillance in 2008 and 2009 confirms an STI-problem among HIV-infected MSM. ...