Myelolipoma (myelo-, from the Ancient Greek μυελός 'marrow'; lipo, 'of, or pertaining to, fat'; -oma 'tumor or mass'; also myolipoma) is a benign tumor-like lesion composed of mature adipose (fat) tissue and haematopoietic (blood-forming) elements in various proportions.

Larger myelolipomas are at risk of localised tissue death and bleeding, which may cause a retroperitoneal haemorrhage.

[5] Recent experimental evidence suggests that both the myeloid and lipomatous elements have a monoclonal origin, which strongly supports the hypothesis that myelolipomas are neoplastic lesions.

[5] Older theories proposing a non-neoplastic origin include the following: Myelolipomas are usually found to occur alone in one adrenal gland, but not both.

The cut surface has colours varying from yellow to red to mahogany brown, depending on the distribution of fat, blood, and blood-forming cells.

Surgical excision (removal) is recommended for large myelolipomas because of the risk of bleeding complications.