Background In 2005, STI centres in the Netherlands started provider-initiated HIV testing policy, in order to decrease the proportion of people unaware of their positive HIV status and to enable interruption of transmission and create more opportunities for timely treatment. This policy gradually evolved towards opt-out HIV testing and in January 2010, this became the official policy within all Dutch STI centres. The effects of the change in HIV test policy were studied and factors associated with opting out for HIV testing were identified. Methods Data from January 2004 to June 2010 from 488 727 consultations registered in the Dutch national surveillance in the STI centres were used to characterise current practices on HIV testing. Known HIV positives were excluded from analyses. Logistic regression analyses were done separately for men having sex with men (MSM) and heterosexuals, to identify factors associated with refusing an HIV test. Results Since 2004, the percentages of HIV testing within an STI consultation have increased significantly from 56% up to 92% in 2009, and further to 97% in the first half of 2010 when opting out was implemented nationally (both p<0.001). STI were significantly more often diagnosed in clients not tested on HIV during their consultation (p<0.001), except in 2010. Using 2010 data, MSM being older than 25 years (OR: 1.8, 95% CI 1.2–2.6), those having STI symptoms (OR 2.2 95% CI 1.7 to 2.8) and those with a previous STI (OR: 1.5, 95% CI 1.2 to 2.0) more often refused an HIV test. For heterosexuals, having had a previous STI (OR: 1.6, 95% CI 1.3 to 2.0), being female (OR: 1.2, 95% CI 1.0 to 1.4) and being younger than 25 years (OR: 1.2, 95% CI 1.0 to 1.4) were independent factors associated with refusing an HIV test. Conclusions Although provider-initiated HIV testing already increased HIV testing rates, national implementation of opting out for HIV testing increased this uptake even more. Standard testing on HIV in every STI clinic is shown to be highly feasible and ...