OBJECTIVES: Overprescribing of antibiotics by general practitioners (GPs) is seen as a major driver of antibiotic resistance. Training in communication skills and C-reactive protein (CRP) testing both appear effective in reducing such prescribing. This study assesses the cost-effectiveness (compared with usual care) of: (i) training GPs in the use of CRP testing; (ii) training GPs in communication skills; and (iii) training GPs in both CRP testing and communication skills. METHODS: Economic analyses [cost-utility analysis (CUA) accounting for the cost of antibiotic resistance and cost-effectiveness analysis (CEA)] were both conducted from a healthcare perspective with a time horizon of 28 days alongside a multinational, cluster, randomized, factorial controlled trial in patients with respiratory tract infections in five European countries. The primary outcome measures were QALYs and percentage reduction in antibiotic prescribing. Hierarchical modelling was used to estimate an incremental cost per QALY gained and an incremental cost per percentage reduction in antibiotic prescribing. RESULTS: Overall, the results of both the CUA and CEA showed that training in communication skills is the most cost-effective option. However, excluding the cost of antibiotic resistance in the CUA resulted in usual care being the most cost-effective option. Country-specific results from the CUA showed that training in communication skills was cost-effective in Belgium, UK and Netherlands whilst training in CRP was cost-effective in Poland. CONCLUSIONS: Internet-based training in communication skills is a cost-effective intervention to reduce antibiotic prescribing for respiratory tract infections in primary care if the cost of antibiotic resistance is accounted for.