Introduction The purpose of this paper is to examine the size and variability of patients' expenditure in the general dental service (GDS) in Scotland during the recent past. Methods Retrospective analysis of individual patient's expenditure drawn from a 5% random sample of patients treated in the GDS in Scotland between January 1998 and September 2007. Three measures of expenditure per patient were used to assess the size and variability of patients' expenditure in the GDS: patient expenditure per claim, patient expenditure during a 12-month period and patient expenditure during the sample period. Results The size of patients' expenditure on the GDS is small relative to non-NHS insurance arrangements and other components of personal expenditure. There is relatively little variability in patients' GDS expenditure. Conclusions The relatively small size and variability of patient expenditure in the GDS in Scotland suggests that the system of patient charges provides some insurance against the cost of oral healthcare. However, a complete assessment of the insurance properties of the system of patient charges would require several other factors to be accounted for.