The accumulation of fluid in a cyst beneath the skin, usually following a surgical procedure in which tissue has been removed, although one can occur as a result of internal injury as well. A surgically effected seratoma most often follows liposuction, plastic surgery, removal of breast cancer, and similar surgeries involving incision and removal of fatty tissues.

Seroma fluid is typically clear and light-colored, composed primarily of serum rather than the whole blood that makes up a hematoma. The simplest treatment for a seratoma is aspiration, draining the fluid with a needle.

A seroma is, by definition, uninfected. If the fluid buildup in a surgical wound becomes infected, it is known as an abscess, a much more dangerous condition.