An otherwise healthy 36-year-old woman consulted our department with abdominal wall pain. She had a history of double Cesarean section, and lumbar scoliosis. The pain was described as cramping and soar, intensifying after physical activity. The painful area was located cranially to the right superior pubic ramus, radiating towards the right inguinal region. Abdominal ultrasound revealed a heterogeneous mass located in the rectus abdominis muscle, in proximity of its insertion. Hyperechoic and hypoechoic nodules were present, accompanied by a mild degree of internal vascularization (Fig. A). The mass was well defined, and could be differentiated from the surrounding rectus abdominis muscle. Dimensions were approximately 2.27 × 1.23 × 3.41 centimetres (Figs. B, C). Due to the sonographic features and clinical history, the diagnosis of endometrioma of the rectus abdominis muscle was suggested. Histopathology after surgical excision confirmed this diagnosis later on.