Information systems (IS) are increasingly important for measuring and improving quality. In this paper, we describe our integrated delivery system's plan for and experiences with measuring and improving quality using IS. Our approach is that for quality measurement to be practical, it must be integrated with the routine provision of care, and whenever possible should be done using IS. Thus, at one hospital, we now perform almost all quality measurement using IS. However, IS are not only useful for measuring care, but represent powerful tools for improving care using decision support. Specific areas in which IS has already been particularly effective include reducing the unnecessary use of laboratory testing, reporting important abnormalities to key providers rapidly, adverse drug event detection and prevention, initiatives to reduce the costs of drugs, and making critical pathways available to providers. The next wave of effort will be to promote widespread use of computerized guidelines, which is likely to prove more challenging. However, the advent of managed care in the U.S. has produced strong incentives to provide high quality care at low cost, and our perspective is that only with better IS than exist today will this be possible on a widespread basis. Such systems make feasible implementation of care improvement and cost reduction initiatives on a scale which could not previously be considered.