A Krukenberg tumor is a tumor of the ovaries that, though it may appear to be a primary tumor of the ovary, is actually a metastasis from another site.

They are named after Friedrich Ernst Krukenberg (1871-1946), a German doctor who first described them.

Although a Krukenberg tumor is most commonly a metastasis from a gastric cancer, this is not always the case. Other tumors of the gastrointestinal tract including, significantly, colon cancer have been known to cause Krukenberg tumors.

Krukenberg tumors always contain mucin secreting signet cells.