A 38-year-old woman presented for early pregnancy ultrasound scanning 6 weeks and 4 days following an assisted reproduction treatment cycle. She had ß human chorionic gonadotrophin (ßhCG) blood level of 10,853 IU/L 2 weeks before presentation. She gave previous history of termination of pregnancy, myomectomy and bilateral salpingectomy. The uterus was retroverted with multiple fibroids and non-homogenous myometrium in many areas. The endometrium was 21.1 mm thick with no intrauterine pregnancy. An initial diagnosis of cornual/interstitial ectopic pregnancy was made. However, 3D images rendering and the multiplanar technique showed a 27.5-mm gestation sac, medial and above the interstitial part of the right tube, with 7.6-mm-long foetal pole. ßhCG and progesterone blood levels on the same day were 19,551 IU/L and 43.2 nmol/l, respectively. The patient opted against methotrexate treatment. An ectopic pregnancy bulging out of the fundal area was excised laparoscopically. Histopathological assessment showed chorionic villi surrounded by myometrium, as well as foci of adenomyosis, reaching the outer serosa. To our knowledge, this is the second case of subserosal intramural ectopic pregnancy to be reported and the first in a subserosal area of adenomyosis.