Conventional reconstruction of the anterior cruciate ligament (ACL) has a high success rate. Computer-assisted navigation systems (CANSs) have been developed to further improve the accuracy of tunnel positioning. What is the economic impact from the hospital perspective? Patients having a first ACL reconstruction procedure were included in a prospective multicentre open controlled study comparing two groups: CANS versus conventional surgery. The primary clinical efficacy criterion was the objective International Knee Documentation Committee score at 1-2-year follow-up. Costs were collected retrospectively nationwide. No significant differences were found for the clinical effectiveness between conventional surgery (100 patients) and CANS (114 patients) at follow-up: ORadjusted 1.01 [0.36-2.84] (n.s). Junior surgeons achieved a significant mean decrease in operating time during the study period: 30% in the CANS group compared with 10% in the control group (p<0.01). The average cost of surgery was 704<euro> for the control group and 1,158<euro> for the CANS group (p<0.01). The cost of the operating room accounts for >70% of the total cost. The surgeon's status and the technical CANS learning effect influenced this cost. The cost differential between the two groups decreased with 'CANS' expertise: 238<euro> and 271<euro> in 'expert' centres versus 427<euro> to 731<euro> in other centres. While our study demonstrates the feasibility and the potential interest of CANS for training in ACL reconstruction, from a hospital perspective it is not cost efficient at present. Economic and decision analysis-developing an economic or decision model, Level II.