['Surveillance for central line (CL)-associated bloodstream infections (CLABSIs) is generally advocated. However, the standard definition of this surveillance does not take into account the number of CLs in place and thus the possibility of increased infection risk with multiple CLs in place simultaneously. In this study, we tested the hypothesis that simultaneous placement of more than 1 CL is associated with an increased CLABSI rate.', 'The number of CLs, CL-days, and CLABSIs and CLABSI rates with regard to the number of CLs in place simultaneously was documented in 2 intensive care units between 2001 and 2011. Standard CLABSI rates, as well as the rates for 1 CL and multiple CLs in place, were calculated.', 'The average CLABSI rate was significantly lower in patients with 1 CL in place compared with those with more than 1 CL in place (3.69 per 1,000 CL-days vs 13.09/1,000 CL-days; incidence rate ratio [IRR], 3.63; 95% confidence interval [CI], 2.61-5.05). Importantly, all differences from the standard rate (5.94/1,000 CL-days) were significant (1 CL vs standard: IRR, 0.61; 95% CI, 0.51-0.74; more than 1 CL vs standard: IRR, 2.23; 95% CI, 1.87-2.65; both P < .0001).'] Does simultaneous placement of multiple central lines increase central line-associated bloodstream infection rates?