Large multiinstitutional databases are excellent sources of information that provide clinically useful insight into the practice of cardiac surgery. Fully informed subscribers should be aware of the practical concerns associated with the management and interpretation of database results. During development of The Society of Thoracic Surgeons National Database, three such areas have become particularly important: the database population, the database quality, and the significance of results. Appreciation of the real and philosophical problems associated with these issues will allow for greater appreciation of the intricacies of the database and will enhance the users' ability to interpret information gained from the database.