As the operator of the National Dose Registration and Information System, NRG has implemented a system for radiation exposure monitoring for the Dutch airlines. The system is based on the use of computer generated flight plans together with dose calculations using the CARI-6M program. Before installing the system a study was performed to estimate the uncertainty in the assessment of the annual dose of the crew members. It was concluded that the proposed system complies with international recommendations on the uncertainty in dose assessments in individual monitoring and that the operational costs of the system are low.