We describe the process of establishing a large database for the investigation of craniotomy infection and the preliminary results of this database. The initial results have been used to generate a cost analysis for craniotomy infection. The craniotomy infections database prospectively registers craniotomy cases taking place in the John Radcliffe Hospital. In order to achieve this, each patient's details are registered at the time of operation and followed up to identify cases of infection. Infection was defined strictly according to Centre for Disease Control criteria and validated by at least two members of clinical staff. The first 10 months of data are presented here which identifies a total of 245 craniotomies and 20 verified craniotomy infections. An overall infection rate of 8% is identified, and the cost incurred by the neurosurgery department as a result of craniotomy infections is estimated at £1 85 660 for the 10-month period studied. This amounts to a cost per case of infection of £9283.