Developing electronic patient records is currently a priority for Health Services, so that the clinician treating the patient has all the relevant information available on the desktop. However, as with paper records, there is the danger of information overload, with key information being missed. It is now recognized that electronic health summaries of patient events will be needed. This paper describes the Scottish Record Linkage system, which has been routinely used over the last 10 years to build event histories for patients in the NHS in Scotland. Probability matching has been used to identify records belonging to an individual since a unique patient identification number has not been in general use. We present examples of use of this rich information resource, either for clinical decision making, evidence based medicine, or population needs assessment, and investigate how the system may be developed in a data-warehousing environment to populate electronic health summaries for the five million residents of Scotland.