A wound seroma is an accumulation of serous fluid in the subcutaneous layer that follows a surgical procedure. Tissue damage and increased vascular permeability result in a sterile collection of proteinaceous fluid in the dead space within the tissue. It typically develops shortly after surgery, but may form a week or two later. If untreated, it can persist for many months. It may undergo secondary calcification. Smaller seromas do, however, tend to resolve spontaneously.

A seroma is usually painless, but mild discomfort may occur. A clear discharge may be present. In the rare case of secondary infection, a seroma may become tender and develop into an abscess requiring immediate medical attention. Other signs of infection include fever and a bloody, malodorous, or purulent discharge.

The most common types of surgeries that cause wound seromas are breast, abdominal wall, and reconstructive surgeries, particularly if skin flaps are created or if a foreign body, such as prosthetic mesh, is introduced.