To determine if the catheter lock taurolidine can reduce the number of catheter-related bloodstream infections (CRBSI) in pediatric cancer patients with tunneled central venous catheters (CVC). During a study period of 34 months, 129 newly placed tunneled CVCs in 112 patients were randomly assigned to standard lock with heparin solution or experimental lock with a taurolidine solution (ClinicalTrials.gov Identifier NCT00735813). Sixty-five CVCs were included in the standard group and 64 CVCs in the experimental group. The groups were comparable regarding patients' characteristics. A total number of 72 bloodstream infections of which 33 were CRBSIs were observed during 39,127 CVC-days. A lower rate of CRBSI (0.4 per 1,000 CVC-days) was observed in the experimental arm compared with the standard arm (1.4 per 1,000 CVC-days, incidence rate ratio (IRR) = 0.26; 95% confidence interval (CI) 0.09-0.61; P = 0.001). A lower rate of total bloodstream infections (1.2 per 1,000 CVC-days) was also observed in the experimental arm compared with the standard arm (2.5 per 1,000 CVC-days, IRR = 0.49; 95% CI 0.29-0.82; P = 0.004). Median interval from catheter insertion until first CRBSI was significantly lower in the standard group (156 days, range 12-602) compared with the experimental group (300 days, range 12-1,176; P = 0.02). Premature removal of the CVC due to infection and overall CVC survival were similar in the two study groups. Locking of long-term tunneled CVC with taurolidine significantly reduces catheter-related bloodstream infections in children with cancer.