Laws vary from state to state, but in some states a health insurance carrier, health maintenance organization, or other managed care entity for a health care plan has the duty to exercise ordinary care when making health care treatment decisions and is liable for damages for harm to an insured or enrollee proximately caused by its failure to exercise such ordinary care.

This liability may be created by a specific state statute or by the state's common law (court opinions or case law) under a negligence theory for breach of the standard of care (reasonableness).

In Illinois, health insurance carriers, health maintenance organizations (HMOs), and other managed care entities are expected to adhere to a standard of ordinary care when making decisions about health care treatments. If they fail to exercise this level of care, they can be held liable for any harm that results to an insured person or enrollee. This liability can arise from specific Illinois statutes or from common law negligence theories, which are established through court opinions and case law. Under these legal principles, if a managed care entity's decision-making is found to be unreasonable and this leads to harm, the entity could be required to compensate the affected party for damages. It's important to note that the specifics of the law can vary, and the application of these principles can depend on the details of each case. An attorney specializing in health care law or insurance law would be able to provide more detailed information about the potential liability of managed care entities in Illinois.