The General Practice Research Database (GPRD) is a col- lection of anonymised patient records obtained from UK gen- eral practices. Data are representative of approximately 8% of the UK population and are collected mainly for research purposes, which include assessing risk factors for disease, evaluating the side effects of drugs and comparing the effec- tiveness of different drugs. The data are used internationally by academics, governments and the pharmaceutical indus- try. As research findings arising from GPRD data may have potential public health and safety implications it is crucial importance that the data collected is of high quality. Data quality may vary within and between practices and may de- pend on the time of data collection. Although the GPRD’s established framework for assessing data quality is compre- hensive, it does not allow a systematic review of individual practice data quality markers. We are developing a frame- work for further improvement of existing methods of data quality assessment. We shall extend a set of current qual- ity measures for each practice and, using statistical pattern recognition techniques, shall develop algorithms that will combine these measures into a smaller number of meaning- ful quality scores which will reflect different aspects of data quality and can be measured over time. We report the aims and rationale of the study and preliminary results