Capillary malformation–arteriovenous malformation (CM-AVM) syndrome is an autosomal dominant disorder caused by mutations in RASA1. Multifocal, small, round-to-oval, pinkish-to-red cutaneous capillary malformations are seen in more than 90% of people with RASA1 mutations. These RASA1-associated cutaneous capillary malformations (CMs) can accompany internal or cutaneous arteriovenous malformation (AVM) or arteriovenous fistula to constitute CM-AVM syndrome. The cutaneous capillary malformations in CM-AVM syndrome are unusual in that some lesions have high-flow characteristics (according to Doppler or a white halo). We describe the histopathologic and corresponding ultrasound and Doppler findings in a CM from a patient with clinical CM-AVM syndrome and show that an arterial component is not present in the dermis or the most superficial portions of the subcutaneous fat but that there is ultrasound evidence that an AVM resides in the underlying adipose tissue.