Background: Arteriovenous malformations (AVMs) are commonly thought to be congenital malformations; however, patients usually present in adolescence or adulthood. This study was carried out to better understand the development of AVMs between birth and presentation. Methods: A retrospective review was performed of the medical records of all patients under 25 presenting to a single institution with an AVM or spontaneous intracerebral hemorrhage from 2000 to 2007. Results: Out of a total of 34 cases, 3 children were identified with delayed de novo appearance of an AVM after an intracerebral hemorrhage and normal initial angiography. The clinical and angiographic features are presented for these 3 patients and for an additional patient with AVM recurrence after complete surgical excision. Conclusions: In the light of these cases and a review of the literature, we suggest a hypothesis that AVMs develop postnatally, undergoing a period of growth in childhood or early adulthood, and that they may become symptomatic from the time of their earliest development. The trigger to growth may be shear stress stimulating growth factor expression by endothelial cells lining an arteriovenous fistula. Alternative stimuli, such as venous hypertension, cannot be ruled out.