American courts generally approach emotional distress claims with caution. Typically, they require a physical manifestation of the emotional distress, or that the plaintiff have been touched physically by the tortfeasor or been in the "zone of danger," or they require expert proof.
Yesterday the Illinois Supreme Court decided in a medical negligence case that Illinois imposes no such requirement. See Thornton v. Garcini, Docket No. 107028, Slip op. (Ill. Oct. 29, 2009). Rather, the rule in Illinois now appears to be that claims for negligent infliction of emotional distress do not require physical symptoms or expert proof. This holding appears to reverse prior holdings in Corgan v. Muehling, 143 Ill. 2d 296 (1991) and Hiscott v. Peters, 324 Ill. App. 3d 114 (2001), which had seemed to impose the requirement of medical expert testimony in exchange for having abandoned the "physical injury" requirement. Thornton, Slip op. at 6 ("we overrule the portions of Hiscott limiting Corgan to its facts and requiring all claims for severe emotional distress to be supported by expert proof").
Now, Illinois law is that the "absence of medical testimony does not preclude testimony for emotional distress," but rather that it goes to the weight of the evidence. Id.