Implantation of an endometriotic lesion within a pelvic or abdominal wall scar is an uncommon but well-described condition that may be the underlying cause of acute or chronic recurrent abdominal or pelvic pain, especially after cesarean section. Radiologists may not consider scar endometriosis when it is encountered at cross-sectional imaging. Cesarean section scars are the most common site of extraovarian or extrauterine endometriosis. The condition also has been identified in other uterine surgery-related scars and in the skin, subcutaneous tissues, and abdominal and pelvic wall musculature adjacent to these scars. The most plausible cause of scar endometriosis is implantation of endometrial stem cells at the surgical site at the time of uterine surgery. Patients with scar endometriosis may be asymptomatic or present with cyclical pain corresponding to the menstrual cycle. Cross-sectional imaging findings vary from the nonspecific to those suggestive of the diagnosis when combined with clinical history. In particular, the presence of blood products in an anterior abdominal wall mass at magnetic resonance (MR) imaging with no other explanation is strongly suggestive of scar endometriosis. Ultrasonography, computed tomography, and MR imaging may be used to depict an endometriotic lesion, exclude endometriosis, or provide evidence for an alternative diagnosis.