In 1994, ONS took over the running of the General Practice Research Database-formerly the VAMP Research Database. As the database had not been widely used for general health monitoring purposes, ONS undertook a study to evaluate the representativeness, quality and validity of the data. This article compares GPRD patient consulting rates for four conditions (chicken pox, hay fever, asthma and diabetes) with equivalent data from the 4th National Morbidity Survey in General Practice; and compares GPRD patient treatment rates for asthma with epidemiological survey data. The results suggest that the GPRD is a potentially useful source of national morbidity data.