Computer-based patient record systems have become very common in the primary health service, but their effects have seldom been documented. Three surveys were carried out in the municipality of Sør-Varanger, in 1993, 1994 and 1995, to discover how such a system has affected the running of the municipal medical centres. The most significant changes were organisational. Certain tasks changed hands, others were dispensed with, and new ones were added. Information on patients became more readily available, and services to the public were improved. Many more patients received an answer to questions concerning information in the case record, and far fewer forms had to be filled in manually. Despite this, computerisation had seemingly led to little change in effectiveness, and the total load of work remained the same. The survey also showed that simple extensions to the system could produce marked improvements.