In 1998, an audit on psychiatric problems in general practice was conducted in four Nordic countries. Five-hundred-and-sixty general practitioners participated and made registration according to the Audit Project Odense method. This paper describes the methodological problems related to international differences in the organisation of health care, recruitment of general practitioners and the registration of contacts. Nordic differences in this audit gave rise to inspiring discussions at national meetings, but methodological problems remain to be resolved if the results are to prove useful in scientific reporting.