Almost all medical malpractice cases require expert opinions. There are numerous rules governing the information that may serve as the basis of expert opinions. Consider the following: Medical experts may base their pinions on first-hand observations, data offered to the expert by patients and relatives and opinions and reports from hospitals and staff records, and facts within the record but not within evidence. Experts may also base their opinions on interrogatory answers, depositions and other expert depositions. Experts may also base their opinions on medical literature and yet the contents of medical literature shall not be disclosed on direct examination. Conclusions must be held to a reasonable degree of medical certainty. Opinions as to what “could” or “might” have happened are appropriate, and the expert can also testify as to what “did” happen. Proving medical malpractice cases involves a significant degree of legal and verbal technicality. A profound understanding of applicable case law is necessary in order to pursue medical malpractice cases in Illinois.