A 29 year old nulliparous woman was seen for prepregnancy counselling with a congenital pelvic arteriovenous malformation. The diagnosis had been established following a life-threatening haemorrhage during excision of a lesion of the left labium majus, seven years previously. The woman had no symptoms. She was taking the combined oral contraceptive pill. Her history included a pelvic fracture 11 years previously which had resulted in a deformity of her bony pelvis. The arteriovenous malformation was palpable on pelvic examination as a pulsatile mass over the left vaginal vault, with varicosities visible from the left gluteal region to the groin and the inner aspect of the upper left thigh.Computed tomography had shown that at the level of the obturator foramen on the left there was a large varicosity occupying the left ischiorectal fossa and extending down to join a mass of tortuous vessels ( Fig. 1) which surrounded and partly eroded the left inferior pubic ramus. It also involved the adductor muscles of the left thigh. Femoral angiography showed that the left common and external iliac arteries were at least twice the diameter of those on the right, indicating significant arteriovenous shunting. In addition, shunting to numerous dilated veins was seen ( Fig. 2). The extensive malformation was supplied by branches of the anterior division of the internal iliac artery, notably the internal pudendal and inferior gluteal, and it was also supplied by the medial and lateral circumflex branches of the profunda femoris artery.The extensive nature of this vascular malformation, together with its osseous involvement (and the fact that previous attempted excision had been associated with massive haemorrhage), precluded further surgery. In view of the known risk of enlargement of these lesions during pregnancy and the potential risk of rupture, the woman was referred to a vascular malformations clinic.It was felt that the angiographic anatomy of the malformation made long term reduction in the degree of arteriovenous shunting by embolisation feasible and that this, together with the lack of involvement of the pelvic viscera, would reduce the risks associated with pregnancy. Embolisation was therefore performed. Several large arteriovenous communications arising from the inferior gluteal, internal pudendal and femoral arteries were selectively catheterised and embolised with N-butyl-2-cyanacrylate with an excellent angiographic result, showing almost complete obliteration of the arteriovenous shunting ( Fig. 3). Following embolisation the vascular malformation on the woman's left buttock decreased both in size and colour, although the varicosities on the medial aspect of her left thigh were unaffected.She then had three successful and uncomplicated pregnancies. All the infants were delivered by elective caesarean section in view of the risk of trauma to the malformation from labour and vaginal delivery. Vascular surgeons were in attendance at the first caesarean section but the malformation was not visualised and no trauma ...