Decisions have to be made about what data on patient characteristics and processes and outcome need to be collected, and standard definitions of these data items need to be developed to identify data quality concerns as promptly as possible and to establish ways to improve data quality. The usefulness of any clinical database depends strongly on the quality of the collected data. If the data quality is poor, the results of studies using the database might be biased and unreliable. Furthermore, if the quality of the database has not been verified, the results might be given little credence, especially if they are unwelcome or unexpected. To assure the quality of clinical database is essential the clear definition of the uses to which the database is going to be put; the database should to be developed that is comprehensive in terms of its usefulness but limited in its size.