Periorbital edema is caused by a variety of agents. Periorbital edema is an uncommon, and therefore fairly specific, physical finding in infectious diseases. Bilateral periorbital edema not associated with generalized edema, eg, nephrotic syndrome, should suggest trichinosis, Kawasaki disease, allergic reactions, and bilateral periorbital cellulitis. Unilateral periorbital edema suggests conditions such as thyrotoxicosis, retro-orbital eye tumor, Chagas disease, insect sting, and unilateral conjunctivitis. EBV infectious mononucleosis is characterized by early and transient bilateral upper lid edema.