We report a rare case of rectus abdominis muscle endometriosis excised under ultrasound guidance. A 36-year-old woman came to our observation presenting an abdominal nodule located in the right side of the umbilical area. Ultrasound of the abdominal wall showed two hypoechogenic nodules in the context of the right rectus abdominis muscle and a fine-needle aspiration, performed under ultrasound guidance, confirmed the diagnosis of endometriosis. The patient underwent surgical excision of the lesions. Intraoperative localization was performed through ultrasonography. In our case, the diagnosis was essentially based on ultrasound scan. Computed tomography and magnetic resonance imaging were not performed. A high-resolution ultrasound is a simple, inexpensive and safe method and is sufficient for indicating surgery. Furthermore, the use of intraoperative ultrasound allowed adequate margins of excision.