Desmoid tumors are characterized by proliferation of fibroblastic cells that arise from the fascia or aponeurosis of muscle. They are most commonly found in the abdomen of adults, arising from the anterior abdominal wall, mesentery, or retroperitoneum. At sonography, desmoids have variable echogenicity, with smooth, well-defined margins. On contrast-enhanced computed tomographic scans, the tumors are generally high attenuation (relative to muscle) and have either ill- or well-defined margins. At magnetic resonance imaging, desmoids have low signal intensity relative to muscle on T1-weighted images and variable signal intensity on T2-weighted images. There are no specific imaging features to distinguish desmoid tumors from other solid masses. The diagnosis of desmoid tumor should be considered in patients with an abdominal mass, a history of abdominal surgery or injury, or Gardner syndrome.