This poster, prepared for the MGH Clinical Research Day 2005, discusses some important considerations regarding the preparation of deidentified datasets. It is a requirement of most NIH-sponsored trials that data be provided for distribution to qualified investigators. Studies involving human subjects face the challenge of preparing a dataset that is both useful and protects patient confidentiality. This is a new area, with few established guidelines; the poster looks at some specific issues that have arisen in the context of dataset preparations done for ARDS Network studies.